What stopped Microsoft from making similar deals? I'll tell you what: lack of care. If we go by evidence, MS only seemed to start re-investing in the Xbox division around 2018. That's when they went and acquired several studios (that people were generally okay with them doing, BTW), it's also likely when they accelerated development on Series X and S (they would have had earlier design plans for 9th-gen prior to this, but I think Series S and that dual-SKU approach were NOT part of the initial plans until much later. I would also say the response they observed from the One S and One X solidified the Series approach, but they would have need until near the end of 2017 to actually gauge that reaction and build from it).
Let's look at it this way; almost all of the XBO 3P exclusives that came from 2013 - 2016 were signed by Don Mattrick near the end of the 360 gen. We can say he started negotiating those deals around 2010 - 2011. That includes games like Ryse, Killer Instinct, Dead Rising 3, Crimson Dragon (IIRC was supposed to be for the 360 as a regular game but got pushed back and forced to support Kinect 2) etc. This is probably also around the time Sony started negotiating deals for what they could (given the PS3's market performance at the time; even if it was improving, they were still getting curbstomped in markets like US & UK by 360) for 3P exclusives on PS4.
Now, since PS4 proved itself to be a rather big success out of the gate, that gave Sony more negotiating power when the time came to start securing certain early 3P exclusives for PS5, but they probably didn't start doing this until 2017/2018. The reason Microsoft did not negotiate for deals of a similar scale is twofold: first being due to their weakened market position in XBO gen, the 2nd being because they most likely did not begin fully designing out their next-gen systems until late 2017. Again, Series X & S mirror One X & One S, but both of those were gambles by MS to regain goodwill and hopefully market share. They would not have pressed full steam ahead on Series X & S until they had enough time to gauge One S & One X reception, meaning they needed until the end of 2017.
This isn't even a wild theory to have considering the first semi-credible next-gen console rumors started in early 2018. And, AFAIK, those were mainly focused on basic performance of the then-unknown next-gen Xbox systems. If MS waited until late 2017 to start pushing full steam ahead on Series X & S development, then that would have limited their ability to go after certain 3P exclusive deals, because they would not have had much in terms of prototype hardware or semi-mature devkits, to provide to 3P developers. We can also infer that, given this possibility, they did not have time to talk with 3P developers in terms of feedback for the Series X & S platforms, plus during that time MS would have needed to focus on transitioning the XDK to the GDK.
As you can see, MS's lack of locking down certain key 3P exclusives was their own fault, for scaling back on Xbox funding in the Myerson years, and not really pushing through in funding until 2018. They knew even then they would be far behind the curve which is why that funding was focused on small studio acquisitions. And FWIW, if Sony were as hungry to "squeeze MS out" with 3P exclusivity deals, they would have locked down timed exclusivity deals for SF6, RE4 Remake, Hogwarts Legacy, Avatar, etc. They didn't.
At the end of the day, MS could have locked down some of these same games, and if you actually think about it, most of the 3P games they have locked down are not massive AAA releases. Deathloop barely qualifies, same with Ghostwire Tokyo, and both of those could be argued are more high-budget AA games similar to Plague Tale: Requiem. Sifu and Kena, as well as Stray, are all AA games. I'd actually say Microsoft have locked in more Game Pass Day 1 releases of 3P games than Sony have locking down 3P AA or AAA exclusives for PS! Just off the top of my head:
-As Dusk Falls (also Xbox console-exclusive)
-High on Life (also Xbox console-exclusive)
-Outriders
-The Ascent
-The Gunk (also Xbox console-exclusive)
-Wu Long
-Guardians of the Galaxy
-Ollie Ollie World
-Ravenlok
-Benedict Crumb
-Replaced (also Xbox console-exclusive)
-MLB The Show
-Crossfire X (also Xbox console-exclusive)
-The Medium
-Scorn (also Xbox console-exclusive)
-Stalker 2
-Atomic Heart
-Persona 5R
If you honestly think Sony have to go out of their way to lock down niche Japanese games from Xbox, then you're insane. And for any 3P exclusive Sony has coming along the way that is already known of, Microsoft have one of their own.
-Sony: Rise of the Ronin
-Microsoft: Contraband
-Sony: Stellar Blade
-Microsoft: Perfect Dark (The Initiative is barely a studio and CD are a 3P dev owned by Embracer Group)
Otherwise all of Sony's other AA and AAA exclusives are either 1P-developed or being done in collaboration with smaller 3P studios not dissimilar to what Microsoft or even Nintendo do. So really, your whole talking point, when we shift through the nonsense, is about Final Fantasy being PlayStation-exclusive. Lord forbid PlayStation has even a few 3P exclusives, even for games they help fund and develop as the FF XVI team themselves have said is the case.
And the hilarious part is, most of the Final Fantasy games AREN'T PlayStation exclusive
. Didn't Crisis Core just come to Xbox and sold like 6% of all sales there? Not to mention historical sales data for FF XIII and XV in terms of console splits, and you wonder why Square-Enix doesn't have a problem working with Sony on mainline FF games in return for them having console exclusivity?