There's such a deep seeded, systemic bias against linux that it actually can never win, to any degree or magnitude, because the moment it starts winning we just move the goal-posts for the flimsiest of reasons to ensure it can't quite claim that victory.
Linux is obviously and clearly the most popular operating system kernel on the planet. Oh, no, that's no good a measure, servers are messy, let's refine it to most popular consumer operating system kernel? Oh... it, could also reasonably claim that title? No no, no Android, that doesn't count. Nope, No Chrome OS either, you can't have that, that's, well, that is linux, but its not. Just nice, pure, desktop linux, yes, perfect, arch linux, kde desktop, that'll never trend up and thus is the perfect new-new definition of desktop linu--wait hold up, I'm getting word this is, not possible, its actually SteamOS? Nope, kill it, that's not desktop linux either, kill it.
So it is proper Linux, as GP comment implies. Yes it's running games in Windows compatibility layers, but it is also a complete Linux system itself, with desktop. Definitely counts as running Linux.
And a decent chunk of those games are running on the Unity or Unreal runtimes. Do they count as "running on Windows"? Where are we drawing the line here?
if the developer released it as a windows build but is being played though a compatibility layer, yes. Unity and Unreal both support deploying Linux builds, but it doesn't mean making a proper Linux port is as easy as pressing the "Linux" button.
>Where are we drawing the line here?
I don't personally care for what counts or not. I just personally wish for more native support.
As someone who has played a lot of games with native linux "support", I want less of it.
In nearly every instance of these native ports, switching to using the windows version via Proton was a better experience, either because the Linux version was outdated, unmaintained and buggy, or it simply performed better.
Annoyingly, as far as I can tell, Steam these days doesn't make a distinction between native ports and Proton games so it's hard to tell if I'm getting served the unloved child version until something goes drastically wrong and I have to start messing around with it.