It's not like they're stuck on some outdated proprietary engine like RPG Maker. Minetest is under active development, with a small list of dependencies that are also under active development. It is under no particular rush to get off of X11/Xwayland.
Individual apps, particularly full-screen games, shouldn't need "Wayland support"(quotes because what that means will vary between implimentations).
Now, if you have to install xorg on a system that doesn't have it in order to play a game? Yeah that would suck, although games are on my personal shortlist of application categories that should always be run from a flat-pack/equivalent and/or containerized wherever possible.
Now I think about it, why don't (anti-cheat)games just run their own VM's and "calibrate" those versus any weird system variables? Seems like a better anti-cheat than hacking-my-kernel-to-make-sure-I'm-not-hacking-the-game...
Even if you use Flatpak, you need XOrg / XWayland on the host system.
Fedora Kinoite/KDE and the KDE Plasma desktop on its own are especially annoying, as I have no idea how to turn off those legacy support services from constantly running, like XWaylandVideoBridge (never used) or XWayland entirely.
I think Windows is just too bloated to also use Containers. With WSL they found a good way and apps should totally run in containers, but this is simply not yet done.
VMs would suck for efficiency as they rely on CPU virtualization and GPU passthrough. The former will never give native performance
Not that hard to stop wayland or xorg at the launch of a given application and restart it at that application's exit. Of course, I only did it on the Raspberry Pi because the hardware lagged horribly running such apps with a gui/compositer/desktop the app wasn't using in the background, but it wasn't hard for me to get working, and its exactly how we did things with DOS apps and even some Windows games back in the WFWG 3.11 days.
Basically, there's no technical reason the host operating system should have to be providing say X, KDE, Plasma, Gnome, Gk, Wayland, whatever, to a flatpack app that needs those things. Yes, the result is a larger flatpack, but that's why flatpack's do dependency consolidation.
Unless ... Unless, you just really want to to run your games windowed with smooth window-resizing, minimization, maximization, etc.