For decades, the standard windowing system was X11; and not just for Linux, for other systems as well. The issue was elsewhere - it provided standardized wire

For decades, the standard windowing system was X11; and not just for Linux, for other systems as well. The issue was elsewhere - it provided standardized wire protocol and you could not break it. It could extend it, but applications not aware of the extension would be not able to benefit. Windows and Mac on the other hand kept the protocol proprietary and you had to use supplied libraries, you could not talk to the display server directly. So Microsoft and Apple could update these libraries; on Linux, there was no such option, all the apps using wire protocol instead of client libraries would be left out in the dark.