I can see why you would think that, but there's alot of stuff unreal just isn't that good at, things like 2d games are a massive struggle to work with in unreal, so it'll gain more popularity, but mainly from devs making 3d games with a focus on high graphics
Alot of the larger instances have user donations set up so that the servers can be maintained, this is how lemmy.world works
yeah, the largest one is k6qw, with 52 thousand users, but only 4 users online atm compared to lemmy.world, 42.8 thousand users, 5.63 thousand online
edit: source: https://lemmy.fediverse.observer/list
@Dawn
@lemmy.world