The Deck is so transformative that if Microsoft were serious about XBOX at all, the next XBOX would be a handheld.
Or they’d realize that the Deck is successful because it’s open and bring Steam to the Xbox.
[1] Personally I remember how bundling ruined the brands of Cable TV which makes GAME PASS seem like a disaster to me, but objectively, the Cable TV ecosystem resisted change for 30 years and only really broke when Tubi came along, so maybe they'd be happy to be the new cable.
There are also apps that let you do it.
Gamers that reach out to handelds in Nintendo Switch numbers don't care about what OS their consoles use, and won't be buying Steack Decks "because Linux!".
Linux doesn't have user experience rules, which is why Steam OS works.
As someone that was part of game development community (Flipcode, Gamedev portals, IGDA), demoscene, before FOSS became mainstream, my point of view is that both communities don't really overlap on point of views towards software and consumer experience.