if they want more, they can always be confused and ask

Thing is, people do, which is why...

I've seen so many posts with multiple paragraphs explaining federation

The easiest thing to do is, obviously, send new people to large sites that already have all of the remote communities people want access to subscribed to. Those work super well for people who need federation to be mostly hidden from them. But there's are practical caps on how big any one instance can get, which necessitates horizontal expansion of the network. Newer or smaller instances aren't going to have as complete federation, and that makes them less than ideal as a place for new users to go.

We need admins who are spinning up new instances to be conscious of this. People making niche instances need to have alts on mainstream instances to initiate federation. People making general purpose sites need to make sure they're seeding their server with all of the communities people want to join. Expansion needs to be done consciously and contentiously to make the distributed nature of things not matter.