I think the instance is not showing because it is not online at the moment... here you can see the stats of kbin.social on fediverse observer https://kbin.fediverse.observer/kbin.social
Regarding the amount of instances and the rather small users/server: a lot of the mbin instances used to be kbin ones (like you can tell by their name) including mine. So we did not start with one central instance that all the users went to, but with a lot that already had a small number of users. And the project itself is not that old, not even a year (we start in September or October 2023). I'd say we really only have one hyperfocused instance and that being rimworld.gallery