There used to be a system which made it very difficult to maintain anything above 20. People still stretched it to 25 but outer regions required a bit of work. This however didn't really encourage any new realms people are thinking about. It only forced big realms to create more puppets which eventually grew quite large.
Many things have been tried but none of them really made people want to create more smaller realms. The main problem is people don't want to suddenly give up everything they've built over the years so others can have fun. It just doesn't happen. If you want this to happen, you need to climb there yourself.
