The options are:
Linux based OS, do a computer to add game of choice to the OS's "capable of being used" list of programs, download game, install game, play game, or:
Window, download game, install game, play game.
90% of people, maybe even more, and not good enough at doing a computer to pull off the linux stuff, and even if they were, some don't want to bother because it adds another layer of complexity and therefore potential issues and things that can go wrong in playing it. Not to mention that the support systems generally frown on using unapproved measures to run things, so if you're encountering a bug or glitch or something, you might not be able to be helped by the developers because you're using it in an environment it's not designed to run in*.
*note: just because the script is "exactly like windows so you're argument is invalid" no, it's not exactly like windows, if it was, it would be windows. Generally this won't cause issues, but the support system cannot verify what's wrong if you're using something they didn't plan for. That's why those clauses exist.