I don't know about the "on Gnome" part, specifically, but I think Ryan has done work on SDL on contract, or contributed to SDL as part of contract work on e.g. game ports. He's a prolific guy with many stories to tell about the Linux desktop, see https://icculus.org/~icculus/
I do get your point, though, and it's true, there's of course a lot of manhours on e.g. app fixes and porting, and many other things, that happen on a volunteer basis in the community to make it all work.
Yeah, Icculus' case is a bit odd but also one of the strongest showing this in action. Barrier/synergy/input-leap (or whatever they're calling themselves these days) is another good example, but I can't just link to one polemic thread to get the point across. They've more or less just given up, despite the like 3 grand bug bounty for getting it working on wayland. Waypipe works, but ironically you can't forward x11 apps so you get into this weird situation where you need to use different protocols for different apps and you don't know which ahead of time.
OBS seems to finally be working with linux/wayland again, semi-reliably, and of course most things continue to work via x11 shims. It's getting closer, especially as Gnome gets closer to actually implementing a full set of desktop app protocols, but it is just a lot of work for toolkit developers to port everything over.
I still don't know how you'd go about running GUI apps inside docker containers, something we do at work for a few complicated deployments of ROS stuff (yes I'd rather do it some other way, but we don't have the man power).
I do get your point, though, and it's true, there's of course a lot of manhours on e.g. app fixes and porting, and many other things, that happen on a volunteer basis in the community to make it all work.