It isn't 'just another' DRM platform. It's in a league of its own with the efforts create a virtual OS-platform to run games indefinitely. That's neither technically nor functionally trivial.
They encourage windows games to bundle old and insecure dlls, which the games generally did anyway. On windows, they don't really do anything here, it's mostly just that windows provides quite a bit of backwards compatibility anyway.
On linux, they do a bit more. They ship a hacked up copy of various libraries from ubuntu 12.04, mostly without security patches, and have the games use those, calling it the "steam runtime" despite it really being "ancient ubuntu libraries". They reduce the security of your machine, and I would only play steam games on a burner machine you don't login to your bank accounts on.
I mean you're not wrong, but games need a stable set of libraries to target. This comment implies they haven't updated those in a decade, but they have releases based on Debian Buster and Bookworm https://gitlab.steamos.cloud/steamrt/steam-runtime-tools/-/b...
The environment for both windows and linux provides unsandboxed acccess to the roaming/home folders, where game saves are typically stored. That's also where your browser's cookies to access your bank are stored.
Many of these games have such fragile netcode that they'll crash even if you don't fuzz them.
