But it kind of is, if the code is so ancient, crufty, and confusing that people don't want to maintain it, which is the case with the X code and a big reason for Wayland in the first place: Wayland was started by X maintainers for the purpose of not having to maintain X. Which they still have to do with Xwayland, but even that will stop as Xwayland was only ever supposed to be a stopgap for legacy applications.
FTFY. There are people who want to keep using X and the only solution to that is to maintain it as code wont be maintained by itself. The entire point of open source/free software is that if anyone wants to fix/implement something they're free to do so, so for as long as someone wants to keep using X and has the necessary know-how (or the time and will to learn), X will be around.