Performance, inclusivity, familiarity. Boils down to these 3 things.
Discussion
+1. The complication of signing up can be made into something exclusive. But the ease of continual usage needs to be better.
I also think it is important to recruit more people, new people. I don't know what was Twitter's breakdown but i am guessing during the early stages it could have been something like a several cycles of 80% fresh blood and 20% retainer and eventually it balances out.