The average person won't jump through these hoops just trying to subscribe to a community. I can clearly see them on a list, but still not able to join a bunch from my instance (lemm.ee). Are they too small? Nobody from my instance on them? Whatever.
I think that if there is no one from your instance (which also happens to be my instance) is subscribed to a community on an instance other than your own then you have to search for it in the search bar (using the url or !community@lemmyinstance) before you will be able to interact with it. Lemmy doesn’t synchronize everything between all instances by default, only what is needed to save on resources.
No one on your instance has subscribed to them, but you still can. Just copy the full link of the community on the instance and paste it into your instances search bar and it may lag but give it 30 seconds or so.
The after that everyone on your instance can discover it more easily.