So, my take:
Nadella's really into subscription-based cloud software. It was his opening salvo to get the CEO job, it brought Microsoft a ton of recent success, and Spencer managed to convince him of the idea of Game Pass by pointing out how well it dovetails with what Nadella likes. That way, they could sell Game Pass as a service to Samsung and TCL and Nintendo and so forth.
(It's also worth noting that Nadella absolutely loves that Spencer bet on Mojang and considers him a visionary in the gaming space because of that.)
My suspicion is that Game Pass was always supposed to be an argument for cloud gaming. They start with downloadable, make a cloud service, and then the audience (in their minds) moves entirely over to playing Like a Dragon on a phone. But adoption wasn't quick and game pass numbers — which they always say are satisfactory but they love to pick and choose by what metrics — were pretty slow as well.
Which meant that Game Pass could not satisfy the goals they had for it.
1) Make enough off subscription costs to offset traditional sales
2) Be a bridge to a cloud service that is on everything
3) Drive hardware with separate Game Pass environments
When you don't satisfy those goals, that means the entire software development strategy has to fall without that cornerstone. You can't afford to make huge games that don't benefit from people buying them to recoup development costs and you cannot take away any of the constantly marketed core tenets of game pass (easy in-out subscriptions for consumers and day one first-party releases) either. Thus, the multiplatform strategy.
In theory, I think it's actually smart. They give up an edge on hardware (where they were doing poorly anyway) in exchange for games that they can sell anywhere to different audiences. But in order to make games that sell on other systems, they have to wait years they do not have and spend money they do not want to spend to get them there. Outside of Call of Duty, I don't see that happening from every arm of XGS.
This is all a very long way of saying they're stuck between a rock and a hard place and my bet is that they load the cannon with everything they've got rather than being precious about exclusivity. This is not inside information, but yes, I suspect the Gears and the Forzas and all that will eventually get ported because they are not getting any cheaper to make and Game Pass is strangling them more than they will admit. Hell, the Coalition was making another game before Gears that they were then ordered to pivot from because Microsoft could not afford to wait that long for a new Gears game (again, that's public, not inside information).
