We have so many options for window managers, shells, desktop environments, distros, and kernel architectures under Linux, but why after (maybe) 20 years do we only have X.org server (including its predecessor) as the bottom layer of GUI?
I know about XFree86, and Y, but most of them are stuck. Is it so hard to create a new (i.e modern) one? Or is there any other reason we are stuck on X.org?

