With the widespread support for Steam/Valve on this forum because of their contributions to making Linux gaming easier, I'm now confused as to why people here are using Linux in the first place.
I personally do so out of support for FOSS software, the customizability, and actual ownership of software, which I thought were most people's primary reasons for using any Linux distro. Steam seems antithetical to all of these. The software in the first place became popular as a form of DRM, and it gets publishers to use it for the allowance of DRM on the platform. The Steam client has the absolute minimum customizability. Your account can be banned at any point and you can lose access to many of the games you have downloaded.
Whenever I game on Linux I just use folders to sort my game library and purchase any games I want to play on itch.io or GoG. On my Linux PC I stay away from clients like Steam because I want a PC that works offline, and will work if all of my accounts were banned. It's more of a backup PC.
Since Steam has every characteristic of Windows, 0 customizability, DRM, plenty of games that are spyware, I see no reason to really not use Windows instead for the much easier time I can have playing games.
Yes, I prefer many of the features of Linux distros, but using a client like Steam defeats the purpose of them. Ridiculous storage requirements due to unoptimized dependencies, having to have a background client running for some games and wasting resources on doing so.
So, why use Linux and support Steam, or use Linux and use Steam?
I'll try and keep it short with a bullet list, as I can tend to be long-winded about everything.
There are some reasons to like Windows, but it's harder to justify with the direction Microsoft is, and has been, moving.
EDIT: To actually answer your question about Steam and Linux... because I have a Steam account that I've had for many, many years with 1000 games that predates me moving to Linux in a more serious capacity. While I could move to GOG (and have), I'm not just going to throw away my game library. But also, Steam working to make gaming more mainstream on Linux is a net positive for Linux in general. That was always the reason many people gave for why they wouldn't switch - that, and proprietary software that won't run on anything other than Windows or maybe Mac.