I think it's likely just tribalism. There is no nuance to the comments, which is a hallmark of tribalism. A more nuanced discussion might make some key basic concessions:

- Windows will have better support in most cases. - Linux users might need to be more technically savvy in most cases. (although most PC gamers are probably technically savvy enough to _use_ linux.) - Windows will usually (but surprisingly not always) get somewhat better performance than Linux in gaming. - etc.

A more nuance discussion might then state that all things being equal, Windows is usually the better gaming platform, however Linux is perfectly viable, particularly if your operating system concerns come before your gaming concerns.