Why? With Bazzite and similar that's kind of the whole point of them existing. Just installing Steam from Flathub or the repo is not going to get the same level of integration (gaming mode, etc.). Bazzite works really well on my PC handheld and I don't think a generic distro with Steam added after the fact would be the same. Id you want a distro without Steam bundled there are lots of those.

It's a quid pro quo from Valve. They are investing profusely in Linux ecosystems, and the distro-devs are following that. Meanwhile Epic Games still lacks a first-party app on linux, and users need to pass from Lutris, Heroic etc...