Being available to the public if they bought the game doesn't mean it's in the public domain and you're allowed to upload a copy of it (or a derivative work) on

Being available to the public if they bought the game doesn't mean it's in the public domain and you're allowed to upload a copy of it (or a derivative work) onto GitHub, though (I like these projects but I really don't think they could defend themselves legally if you company went after them)