It's because Apple told Steam users to fuck off like 3 times in 5 years (nuking 32-bit support; no Vulkan/OpenGL support; switching to ARM). Users and game devs got the message Apple was sending loud & clear.

32-bit is the only change that actually broke anything, and it had been deprecated for a decade.

64-bit OpenGL/x86 games work fine on ARM.

Will x86 games work in 2 years? Will OpenGL? What about in 3 years? 5? Then what happens to Valve's Apple owning customers purchases?

Apple killed support for legacy 32-bit applications a good while back, which killed support for virtually every Mac game port.

The funny thing is most games in my library say they won't run on macOS because they're 32-bit applications, and they won't show up in my library when filtering by "Mac". But they all run perfectly fine, so they're obviously 64-bit. I think I heard once that they all default to 32-bit unless the developer says otherwise...

I'm sure it doesn't make a big difference but the issue with this is it doesn't count Mac users using CrossOver/Whisky because they get detected as Windows users, while Linux users with Proton are reported as using Linux.

From what I’ve seen, for some reason, the people who buy a Mac are not the people who game. College students buying for schoolwork, business people buying for (I assume?) excellent battery life and resulting portability, and graphics/video/music creators. The two Venn circles just don’t overlap.

I play games on my Mac, but I don't use Steam. I just play World of Warcraft which is a native Apple Silicon game, and a few other games that don't require Steam.