The HL3 memes don't even seem fair to use anymore. I don't even want to un-seriously make joke fun of them at this point. They are just genuinely doing so much for the community.
Targeting Wine/Proton is the best of both worlds for everyone. Developers need to Just™ not use a few footguns that they mostly don't have reasons to touch anyway, and otherwise they don't need to change anything, while consumers get a game on that works just as well on Linux as on Windows.
Wine meanwhile works perfectly with 80+% of games, and those 20% that don't are all newer stuff or stuff that's never going to get a Linux version short of the Linux desktop actually getting of the ground.
Also Microsoft Games Studios owns enough studios to make an impact.
Also Proton means zero game studios have to care Steam OS exists, they target Windows, use Visual Studio, and Valve is the one that has to make the needful if they care.
The same studios might even be using game engines that support GNU/Linux, yet letting Valve do the work is much more appealing.
Microsoft has been absolute dogshit at releasing newer program APIs for developer to use. Wine doesn't support UWPs/appx just because there's no demand, since no-one uses the Windows Store. You expect that same Microsoft to get game devs to jump on their new DRM scheme?
Microsoft released even their darling Halo in 2020 and 2021, and have committed to release Halo: Campaign Evolved in 2026 on Steam. I can't think of any new titles under the Microsoft umbrella that hasn't also released in Steam. They've realised that battle is lost. They can change course, but that doesn't mean they'll get anything out of that.
Developers are already doing sanity checks and patches specific to SteamOS. That trend will continue if SteamOS or Linux gains ground. It doesn't matter that the foundation is Microsoft, because even if Microsoft goes bankrupt tomorrow, that foundation doesn't disappear, and even the most malicious Microsoft can't unmake reimplementations or translation layers of their APIs.
That same studio would prefer to make a stable Windows version than an unstable Linux version that might not even work in 5 years since it used some stupid dependency. ANd if they're sensible about it and do a sanity check with Proton, Valve doesn't even have to do any work for them outside of what's already been done.
WinRT now runs on Win32 side as well, that is what new APIs like Windows ML, the abstraction used for all kinds of AI infrastructure now use, just as one example.
Microsoft Games Studio will do whatever they need to make shareholders happy, and if Steam gets in the way of XBox handhelds, maybe a change of heart will take place.
Who knows, Valve is the one that needs to worry, not Microsoft, they control the technology.