I read this as “SteamOS is bad because of reason I personally don’t like that many people don’t understand, so do more research about Linux”
It’s easy to dismiss this as something that won’t ever matter to you, but this is something that can cause problems in all sorts of ways even for gamers. The first thing that came to mind is not being able to install custom drivers to support weird hardware, like a racing wheel or something.
It’s not simply “some strange reason”. There will be a lot of press coverage when they release a desktop version so naturally they want it to be as good an experience as possible. They may not ever get another chance for that kind of coverage after all, and they wouldn’t want SteamOS’s reputation to be damaged (again) because it wasn’t good enough for most people to use (again).