> Does anyone know or have theories why Valve is doing all of this work?

I believe the running theory has been that it's a defense against Microsoft being Microsoft. If MS tries to do something like force all NT apps through their own store and take a cut of every sale, or anything else that poses too much threat to Valve, then Valve has an escape hatch in the form of Linux support. "You want 30% of our sales? Screw you, we'll tell our users to switch to Linux!" is a bit extreme, but it just needs to be a deterrent.

And they will get as many to switch as when DX 10 was only Vista, and other hurdles announced as the opportunity for GNU/Linux take over the gaming world.

Linux dominates mobile, supercomputing, servers and embedded.

There is no fundamental reason why it can't eventually take over gaming, or even desktop.

Android and iOS dominate mobile.

The kernel used by Android is completly irrelevant to userspace and can be changed tomorrow at Google's will, and only OEMs and rooted devices will actually notice it.

On embedded there are plenty of OSes to choose from, with FOSS embedded industry support moving to MIT/BSD licensed kernels, as OEMs don't want to deal with shipping GPL code on embedded devices, specially after v3 happened.

The fundamental reason is that there is no big company pushing Linux on the Desktop. The Linux Desktop community has thus far proven, if I'm being frank, completely retarded at making anything people actually want to use.

It's not as bad as you say. Ubuntu has made a decent attempt, with some (albeit minor) success. But Ubuntu seems to be moving away from desktop to also focus on cloud stuff. Valve has done a lot of work with Windows compatibility.

One thing I'm observing is that macOS and Windows are basically regressing to have the same type of nonsense and quality issues that are indeed typical on desktop Linux. It's possible (but not certain) that they'll eventually cross paths. Linux might not take over the consumer desktop market (unless it's under a proprietary shell, like Android / ChromeOS), but Linux could possibly take over the high-end/power user/workstation market.

Maybe, but that will still either require some big player to come in and make sane decisions to tear the Desktop portions away from the garbage way they're done now, or for the community to get it's act together. I have been waiting 20 years for the latter and do not expect it to ever happen at this point.

Steam would cease to exist and so would the thousand dollars worth of games people have accumulated in their accounts. As long as proton works there is a huge incentive to switch.

I bet that would happen as much as the massive gamer migration that has been going on since XP, which is to say, not really.

Their streaming service can easily use Linux, like Google does with Stadia. That would be a very obvious way to benefit from their own investment into Linux gaming ecosystem. Especially, since unlike Stadia, they are aiming at making their whole catalog work on Linux, using Wine (Proton) and etc.