Display independent DPI scaling. For instance, if you have multiple monitors of different sizes/resolutions, you can scale them independently to have text and windows appear the same size on all of them.
Different DPI per display is the big one. A security story that isn’t ¯\_(ツ)_/¯
That wasn’t really true of Xorg for decades to begin with unless you were using some XMotif applications. Other frameworks’ output is predominantly just bitmaps, good luck using that over anything other than local networks. That problem has a better solution, there really is no reason why the display manager should try to solve it (badly).
I believe Simula is built on wayland due to some wayland specific features
So? Clearly we don't need them for anything important, since we've managed without them up until now. That isn't true of the features that X has but Wayland doesn't.