There isn’t such thing as a WM under Wayland. There are only compositors which make up everything such as the WM, Effects compositor, io etc. To standardize things for smaller compositors things like wlroots exist. Creating a basic compositor using that is around 100 lines of code
They control the ecosystem in the way that they provide what hardware is new on MacOS and what capabilities it has. So if any developer wants to support modern devices they have to port to that new hardware. They don’t have any choice, if they want to stay relevant.