Hive can handle a lot more than it has now. It is just silly to create so much bloat for a handful of users.
As for why people are not bringing on users, because it is extremely difficult and time consuming. It is unlikely anyone will make $200 a day in post rewards consistently (required to get $100 in author rewards). Even that is t squat compared to what well known users can make elsewhere.
RE: Boiling down short form content on Hive