Also XWayland has many limitations as X11 does.
If an app has only ever supported X11, then it probably doesn't care about those limitations (the apps that do care probably already have a Wayland version). And if an app doesn't care about the extra stuff Wayland has to offer, then there's not really a reason to add the extra support burden of Wayland. As long as they work fine in XWayland, I think a lot of apps won't switch over until X11 support starts dropping from their toolkit, and they'll just go straight to Wayland-only.
Wine and Proton have actually put a ton of work into Wayland support, it's very far along. I wouldn't be surprised for Proton to have a native Wayland version soon.