I think its been a long, long time coming. X11 was effectively left in "hard maintenance mode" in the early 1990s when the Unix vendors abandoned the workstation market. Since then every new system based on *nix has used some other display manager, while Linux desktops used X11 mainly for legacy reasons. At some point 10-15 years ago, Linux vendors (Redhat) revived X.org. But something better has wanted for a long time.

"X11 is the Iran-Contra of graphical user interfaces" as the old unix hater book said decades ago.