We know why. No 1st party support from the second half of the 360 era. No console/genre/generation defining games since then.
GP just killed any hope the brand had because it devalued everything the consoles had. Phil sold the idea of huge growth and none of it panned out. In fact, not a single one of their strategies worked.
I know where this is going. PC and Sony too. Xbox started dying long before PC releases.
I don't dispute any of this. That said, I have never said Day 1 PC was the only cause for Xbox's decline in console. It started small with things you mentioned above, and grew over time, with new mistakes amplifying the impact of earlier ones.
Even with no excellent games, day one pc releases for all 1st party games, Xone still sold close to 60 million units last gen.
That's because Microsoft didn't do Day 1 for all games until 2020. They started testing it in 2016 and gradually did it for more games, but it wasn't for the full slate until 2020.
That also coincided with them bringing all their games to Steam IIRC. Sea of Thieves for example wasn't on Steam prior to 2020, it was a Windows/Microsoft Store exclusive on PC up to that point.
Compared to other things they did, PC releases had much less impact than you make them out to have had.
If you're just going by measure of time, then yes the Day 1 PC stuff (and prioritizing user experience for PC at the increased expense of the console) did less to hurt Xbox than other stuff by virtue of happening later.
However, the impact perceived by portions of the fanbase probably made it feel significant over time, because it compounded on mistakes made years prior, and the effect of earlier decisions that had years to fester & take root, magnified newer decisions like Day 1 PC.
Sony isn't going to be impacted by releasing games after 2 years. That's just twitter wars ammo. The general public neither knows or cares about it. They're not gonna build a $1000 PC (minimum) to play their games 2 years later.
The general public aren't the ones who buy their new games Day 1 at full price. It's the hardcore & core enthusiasts fans, a subset of whom not being small and likely also have a 2nd core gaming device like a PC. And a subset of that who might be core enthusiasts of the brand but not necessarily enough of Sony 1P games to feel they have to buy them Day 1.
Even if that portion of the market is only 2 or 3 million out of the 100-something normal million, that can have some impacts on latter-period console sales because the way and rate hardcore/core enthusiasts buy hardware and games early on influences a lot how the wider market adopts the platform later on.
A 2 year delay on PC releases won't harm PS. What will harm them are botched situations like the HD2 one and potentially day 1 releases for all their games. That's when it not only impacts them as a company but us as consumers as well.
2-year stagger windows
WILL hurt PlayStation to some degree upon those who are enthusiast enough to play Sony 1P games and other 3P games, but not hardcore enough to feel they "need" to play those games Day 1 if they can wait a bit later. For example, maybe because they have a backlog to work through, or there are 3P games they'd rather buy & play first. That virtue of patience increases the more platforms a person games on, especially if one of those is PC/Steam.
It's just that it won't have AS much an effect as Day 1 would...but there's also no guarantee Sony don't move in that direction. Do I
think they should? Absolutely not. But is there a chance they will going forward, even as soon as this year? Yes, there is a chance.