Because the entire linux graphics community uses the same API (GBM) and wayland is mostly built around that, but Nvidia insists on not using it for some reason.
Yes, but why is it not a problem for X.org? Can't Wayland be made to work using whatever Nvidia is currently providing? I guess I read it is, and even something (KDE maybe?) made it possible to run Wayland under proprietary Nvidia, so I don't really understand what's the problem.