I can understand they want to test their GPU drivers only against the main Wayland compositors. Xorg is quite another beast to support. For all I know, it might come into the context when most bugs have been ironed out in the GPU drivers.
I do hope people do not take it as general advice. Not all desktop environments have a Wayland compositor, some are quite buggy and many apps don't work yet with Wayland. I am using Xfce and for the next year at least I will be on Xorg. I do hope Wayland gets better, but it has been an undertaking of many years already. The rest of the process won't be much faster I suspect.