Because they didn't work. There should be a feedback loop, not just feed-forward.

N^2 didn't work either except for a few who collected early.

No. Churn is huge, and only a fraction of registered users are active.

Count the alts and people who created alts but barely used them once upon a time and it isn't so high. There are strings of usernames created but never posted. There are alts created for things like zappl that posted a couple times and then were forgotten etc. The churn isn't as high as people make out. There aren't many active users though, you are right there.