Well the other side of that is managing software with hundreds (if not thousands) of person-years of development over it’s lifetime is also hard. There is a sunken cost fallacy with X11, and X11 was constantly extended to be what people needed it to be rather than the best design for the problems arising.

Having said that, I’m not sure Wayland is the ideal solution. X11 doesn’t get in the way of solutions to problems, while Wayland really does. We needed a new and modern display server, but the Wayland project has decided to make that quite restricted - I personally think the security model is too far in the other direction from X11.