A common confusing Linkedin post that doesn't seem to align with established data. The Reddit link doesn't tell us anything about platform splits.

It's probable that PC GamePass has been comfortably outgrowing Xbox GamePass which may have actually declined in the last two years, but I doubt it's close to it yet, even without GamePass Core in the equation. The majority of active Xbox users are on GamePass, and the active userbase is a lot bigger than hardware sales suggest.

Some weird accounting shit is probably going on in this Linkedin post lol.

My thinking is that PC sales have not been majorly significant for them, and they started worrying that they might go the way of Xbox if they keep going like this. It's basically the same question, why have a Playstation/Xbox if you can get everything on PC.
They know that Nintendo's success is based mostly on exlusives, it's a first party machine. So they are thinking, don't be like Xbox, be like Nintendo and you will survive.
Of course, for that to happen, they would need to wisen up and start doing what they used to be good at and release the kind of games they built their reputation on. This travesty with GaaS needs to fade out, at least insofar as it significally hinders developing single player games.

I wonder how much their games were pirated on PC? Could that be a factor too?

I would say that is extremely unlikely, basically a non-issue IMO.

This is a shame since other than Nintendo games PC had basically everything at this point. It does make me more reluctant to get something like Ghost of Tsushima now knowing the sequel won't be coming, at least not till a potential 2nd reversal which wouldn't be anytime soon. It will give the PS6 a notable advantage in that it'll have all big blockbuster games other than Nintendo games now with Microsoft bringing their games to Playstation. Sony could have a hard time finding strong selling points for the PS6 so this would help with that. It's an interesting shift from a few years ago when PC was the only one getting both Playstation and Xbox games so was the platform to get to experience all big games other than Nintendo.