I'm questioning the idea that people should be writing compositors at all. Why doesn't Wayland itself do the compositing and let everyone else just manage windows?

It's like going to Taco Bell and they make you grind your own corn for your tortillas.

Why? Probably better to ask the Wayland developers that. Maybe you're right. That said, whether everyone uses the same compositor and window management is modular, or not and shared code travels as libraries, I don't think the complexity of color management is much different.