From what I understand – which can be wrong! – a couple of different things may cause this:
- People don't know they should check whether a community already exists, before creating it.
- People search to see if the community exists, but it doesn't appear in the search results of the instance/server they live in.
- People see that a community already exists, but they aren't happy with it and create their own.
It's a bit confusing, and unfortunately it causes fragmentation.
Now you made me curious. I've never read the manga. Cheers!