Valve is just hedging against Microsoft having a big red button to kill Steam. They've built their kingdom on top of Microsoft, and Microsoft would love to have it for themselves I'm sure. It's in Valve's best interest to divorce themselves from Windows to protect themselves from Microsoft.
It happens to also benefit the Linux gaming crowd, but it's still ultimately self-interest driving the work. The engineers doing the work are probably doing it for the altruistic reasons, but ultimately Valve is writing the cheques.
Sure, but Qualcomm upstreaming their support to mainline would also have broad benefits for them and be a win-win.
Their C-suits & bean counters are seemingly just not getting that themselves nor having anyone that knows that high enough the hierachy...
What makes Valve great at the moment is that their business interest often aligns with ours (e.g. on the Linux support front). Which is great, don't get me wrong. But that's still beneficial for the company.
It's in Valve's interest to have their own OS and not rely on a rival's platform. Especially a rival that has proven many times they WILL abuse their power.
None of them are on the game for the well being of the community or whatever.
Profits and lower R&D costs, that is all.