Recent testing revealed that Arch Linux, Pop!_OS, and even Nobara Linux, which is maintained by a single developer, all outstripped Windows for the performance crown on Windows-native games. The testing was run at the high-end of quality settings, and Valve's Proton was used to run Windows games on Linux.
You’re right and it’s a pragmatic approach to the problem. They only need broad technical effectiveness to change user behaviour.
I’d argue that it’s not strictly cost cutting but cost transferring. The total client resources most likely exceed that which would be needed on servers.