As already mentioned, the most popular titles on PlayStation are multiplats as well and arguably one of the biggest reason for PlayStation's runaway success in many places was and is historically getting marketing rights for major multiplat games if not outright making them exclusive like they did in the PS2 era with Grand Theft Auto.
Moreover, you're massively downplaying how fucking big Halo 3 was for it's time and how big Halo as an IP was in 2007.
Halo 3 was the best selling game in the United States in 2007 700k outselling wiisports (4.82 million for Halo 3 vs 4.12 for Wii Play). As well, as of 2007, Halo 2 was the 5th best selling video game in America. Only beaten by Madden 06/07 and GTA San Andreas/Vice City. Having sold 6.3 million units despite the
original Xbox only having an install base of 24 million globally. Relative for the time period, those are utterly insane numbers in the United States. Halo 3 was a cultural phenomenon, and it did so being exclusive to Xbox. It had, at one point,
one million concurrent players in 2007. Absolutely insane numbers for the time.
In comparison, Skyrim is the only Bethesda Game Studios game to reach that level. Of course the gaming market by 2011 had grown over what it had been in 2007, and overall, Skyrim did smash Halo 3 in terms of sales. However, a caveat, Skyrim was multiplatform meaning it wasn't just on Xbox (despite that being it's strongest platform in terms of sales) and it had sales of the PS3 (despite the more or less broken port) and more importantly PC. More importantly to repeat is that Skyrim is the only BGS game to be on this level of phenomenon. Fallout 4, while large, was beaten out by The Witcher 3 amongst critics and audiences. Fallout 76 was a disaster.
The idea that a BGS game, on it's own, should be on the same level of system mover and phenomenon as Halo 3, was always ridiculous. We are over ten years removed from their only true Halo 3 tier game, that being Skryim. Since then their stock and reputation as a developer has gone down. There's more skepticism, dismissal, if not outright hatred towards the developer online. While online isn't everything, their more mixed reputation does seep in to the overall consumer base concious. Moreover, they haven't released a single player game in their style since 2015. Nearly a decade ago. Their games may sell, but they're not necessarily a sales juggernaut of the Skyrim anymore. They certainly have a lot of fans, but also a lot of detractors at this point.
Then we get into Starfield itself as a game. Starfield is not only a new IP from a developer who's reputation and sales potential isn't what it used to be, but it's also significantly more niche as a genre. Taking queues more so from hard science fiction such as the expanse then more popular soft science fiction if not science fantasy. IPs Star Wars. Hell, it's even worth mentioning that Mass Effect, despite having a more soft sci-fi space opera, still sold less then all Dragon Age games. Fantasy outright sells more then sci-fi, especially sci-fi works closer to hard sci-fi.
This decreased reputation also stands in contrast of those new IP hits you mentioned. Cyberpunk 2077 was off the back of the runaway success The Witcher 3, and released only 4 years after that games last expansion pack. It had an extremely strong marketing campaign so it was continually in the public minds as well. In comparison to Starfield who's marketing campaign only really started last month. It was building off a strong reputation CDPR already built along with an insane hype train. It also had it's legs easily cut in half due to extremely poor 8th generation console ports, the general bugginess on all platforms, good but not amazing critical reception on the platform it did run alright (PC), and a misleading if not extremely misleading marketing campaign (although I'd argue that the hypetrain made up a lot promises that didn't exist but this isn't the time or place to really have that debate). And now their stock as a developer is down and their next game isn't guaranteed to be a sales juggernaut.
The Last of Us followed Uncharted 3, an already very popular series. As well, Naughty Dog retained a strong reputation through that. TLOU is also zombie fiction, something that was still very popular in 2013. It was also one of the best reviewed games of the year and the very definition of a critical darling. Being one of the games gamers pointed to that games could be art thanks to the fact it was aping cinema, and doing so well. Which is important, it was a new IP that had an unique spin on a popular genre that was also extremely well received at the time.
Elden Ring, despite being a new IP, is culmination of FROMsoft's Dark Souls series. A series that had only grown in popularity with each entry. Dark Souls 3 smashed Bandai Namco's record for fastest selling game until Elden Ring itself. Furthermore, the Dark Souls series only gained more popularity as an IP as the years went on and FROMsoft's reputation and stock as a developer only grew. Mixed in with insanely good critical and consumer reception and the game did extremely well. Uniquely so for a new IP as well. Also, in comparison, Bloodborne and Sekiro, also two new IPs from FROMsoft did well, but didn't do as well as the souls games.
Moreover, none of these three developers had a mixed reputation in the gaming sphere. Neither within the sphere of critics or audiences. They also all released in decent time between other well extremely well received titles. CDPR had the Witcher 3, which only gained in popularity as the years went on. Naughty Dog had the Unchanrted Series. FROMsoft had Sekiro. BGS didn't have any of that. Their last release was Fallout 76, a disaster. A disaster which only made detractors of their games louder. Prior to that, a whole eight years ago, they released Fallout 4. A game that is well liked with a strong fanbase, but it wasn't the biggest title of the year. It wasn't
the critical and audience darling. Hell, Fallout 4 was certainly the spark of making people significantly more skeptical and less super invested in their releases.
It's also worth mentioning that the biggest new IP hits you listed, only one was exclusive. Said exlusive also being, relatively, the weakest performer of all the games you mentioned. Furthermore, they are some of the few exceptions of being new IPs that utterly break out like that. To go back to Sekiro and Bloodborne for FROMsoft. Both were new IPs that did well, Bloodborne especially for being a PS4 exclusive, but weren't the same level of breakout hit as Elden Ring. Both doing worse then the each consecutive Souls game. Games that were based in an IP growing in popularity. A big developer doing a new IP doesn't have a huge chance of being a breakout hit, it just has an elevated one from the normal relatively low chance.
It's honestly getting very annoying how you seem to gleefully remove all context behind why certain games do well in order to push your idea that a BGS should be a Halo 3 type release for Xbox. BGS certainly had a lot of stock at one point as a developer, but it doesn't have that now. It's not 2011, they didn't just release Skyrim. They released Fallout 4 and Fallout 76 in between Skyrim and Starfield. Games that worsened their stock, reputation, and sales potential as a developer. The idea it was "reasonable" to expect a Halo 3 like monster from Starfield should've always rightfully been pointed out as foolish. The contexts between the two games just don't match up. It's an utterly reductionist view that just straight up doesn't line up even with a reductionist view of reality. In a reductionist view of reality, BGS is a developer who's reputation has gone down over the past decade, who's doing a new IP separate from their other large IPs, which lowers the chance of being a break out hit.
Starfield is a new IP in a less popular genre. It's being published by a developer who's sales potential and reputation has gone down in their prior two releases. Post release, the game met pretty good, but not excellent reviews with critics, and a love it or hate it reputation with consumers. Along with a borked PC port that's missing some basic Quality of Life settings and just ran worse on NVIDIA hardware, the hardware the majority of PC gamers use. While also being generally taxing.
Also, while I'm here, your idea that Xbox having a consistent output of well received exclusives doesn't move the base line in comparison to a single big exclusive, to me, signals you don't actually really know what you're talking about. The biggest hits on PlayStation are multiplatform as well, but those exclusives add extra value to the platform. Sure, you can play multiplatform games on Xbox too, but you would be missing out on exclusive titles like God of War 2018 and Ragnarok. Or the Last of Us 2. Or goddamn Spiderman. Getting an Xbox is simply a worse value proposition when you factor in exclusives. Even if you only play multiplatform (which PlayStation mostly has the marketing rights too which associates those IPs to the platform btw) games, PlayStation has those exclusive games you can't get on Xbox and on their own are large IPs (Goddamn Spiderman).
So, ergo, Xbox getting a more consistent stream of well received exclusives. Games you cannot get on PlayStation, does change the baseline because they add value to the console. Rather then just being a less enticing PlayStation that doesn't have the same level of clout of exclusives. As the number of Xbox exclusives grows, and if their well received, that adds value to the ecosystem. Individually they not might move things that much, but collectively they add value to the ecosystem. A reason to purchase a Xbox. Making the platform more then just a worse PlayStation with it's own ecosystem of exclusive titles and IPs.
They don't need to all be very big hits either for this to happen. All of them being big hits, which is what you insinuate by pushing all of Xbox's future exclusives into one "those exclusives" bundle, would of course, massively change things. But a few or even one or two being big hits already pushes things. It would give Xbox it's own identity separate from the one it has now (worse PlayStation more or less). It's own exclusive titles. It's own reasons for owning the console. They all contribute to making the Xbox platform more then just a worse value PlayStation platform as I keep repeating. That does increase/change the baseline of XBS console sales. Starfield, on it's own, does help.
Also, to round this off, even with it's less then stellar overall reception (great but not exceptional from critics and love it or hate it from consumers), it did move consoles. An exclusive BGS game did move consoles. It is something you can't get on PlayStation, it just isn't the same level of megaton as Halo 3 was. Expecting to meet that would simply be ignoring all context between the success of Halo 3 and the current general consumer sentiment around BGS. Which, is what you ultimately did.
And honestly, very few exclusives are the same level of megaton as Halo 3 was for the 360 back in the day. Halo 3 was a fucking juggernaut of a game