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.
Linux "won" the server. Linux has not "won" the consumer desktop/laptop gaming market.
SteamOS is super interesting. Does it count as Linux? Yes and no? Depends on your goalpost! If I were shipping a game today I would 100% support SteamDeck and SteamOS. I'd maybe provide support via Win32 emulation, or maybe native. I'd probably stick to Win32 and only do native if needed for performance.
But I would 1000% NOT claim to support "Linux". I would support SteamDeck and that's it. If any user reported a bug or issue on other Linux distros then I would close the bug as "not supported". If it works, cool. If it doesn't, that's cool too. You're entirely on your own.
Supporting one Linux distro on one piece of hardware is pretty easy. Supporting all the Linux flavors on all possible hardware configurations is a bloody nightmare. And it's radically harder than supporting Windows across all hardware configurations. And it's definitely not worth it to increase sales by ~0.5% or so.
Take from that what you will.