If someone runs Linux Desktop without caring that it is Linux, it still means that they use software that runs on Linux. Say if governments move to some Linux distro, they will need an office suite, and they may pay for its development.

If someone runs SteamOS, it means that they play games on Linux. So it becomes interesting for game devs to test for Linux. And then if someone runs SteamOS, instead of a dual boot with Windows maybe they just go to the Desktop mode. Which means that instead of Microsoft Office, they use something that runs on Linux, etc.

This is good for the Linux ecosystem. And the reason I like the Linux ecosystem is because, as you say, it's not fully controlled by TooBigTech.

The alternative to Microsoft Word isn't LibreOffice Writer, it's Google Docs, which is very much controlled by a big tech company.