They don't do this on Linux because there's no unified way to do it on Linux. It also happens on macOS if memory serves me right, but macOS makes it aggravating enough for people to usually disable it because of that (you can't do a silent application launch when logging in on macOS from what I can tell - sole exception being iTunesHelper on older versions - so any browser that sends push notifications opens a new window when you login to the computer, making it obvious and annoying).