@Gargron two things come to mind :
- half-life of accounts in .social, meaning, after X months, people are forced to create an account elsewhere and move. This solves the issue of uncertainty when signing in
- demo mode : I feel like a huge number of sign-ups in masto.donte.com.br were people wanting to check out what was mastodon after all. So they do and they drop out, if there was a demo instance, maybe it would solve this