It is only one old C codebase however (or a couple if one counts the *BSD semi-forks separately) instead of many different fresh c codebases (one per compositor with some shared code between some of them to be fair). I don't buy that this is actually better for security. It is a lot of more fun/less painful than cleaning up and improving some legacy codebase however.
There's nothing that forces a Wayland compositor to be written in C. I've seen ones written in C++, Zig, and Rust, but you could really use any language as long as you can still call the appropriate system/kernel APIs
Nothing preventing you from writing a X11 server in something else either (and people have done so!). But fact is, most wayland compositors right now are either pure C or C++ (and I think the rest uses at least wlroots?).
Many X11 window managers are written in non-c languages too and I don't think I am too far off the mark when I say that a decent fraction of wayland compositors would just be external window managers if there existed a standardized interface for window managers when they were written (I think some compositors have an interface for external window managers now, but is there a standard interface by now?).
