A lot of their tooling and favored software works by being as minimal as possible while doing its one primary purpose well. They dislike monoliths like systemd, pulseaudio, networkmanager etc. which do many tasks. The wayland protocol itself is fairly minimalist, which they seem to like, but to practically use it you end up requiring a monolith compositor/window server.
Further, Wayland fundamentally doesn't support running e.g. in a non-compositing mode, and requires more cruft to draw to the screen vs just using xlib.
At the end of the day, all the functionality that Xorg provided has to be served by something. And when you're not using one of the big boy software stacks like Gnome or KDE, that means re-implementing the wheel, or copying from another project like wlroots. I suspect they prefer the status quo in that Xorg is at least proven and fairly battle hardened software.
Just idly guessing, though.