Steam on Linux defaults to providing a container based standard Linux environment which is independent of the underlying OS, providing access to all the expected software libraries and OS calls that games need to run.
This is integrated into SteamOS. It's also available via Steam on any other Linux distro. (And if you wanted to you could cut that part out and run it without Steam.)
When running Windows games it even runs Proton within this container environment.
That gives you a single very predictable and version controlled software environment.
Meanwhile Windows randomly deprecates stuff that somebody might have invested tons of development effort into (silverlight, mixed reality, etc)