@pixel
I may be naïve, but why wouldn't they survive? Do you mean just recently set up ones, whose maintainers might decide it wasn't for them after all? Established ones can just cut off new users if they're getting too full or too much traffic, can't they? I would think server load would scale about linearly with users on the server, so that works?
@ceoln A few reasons - definitely admins that decide it’s not for them for whatever reason (too much work, changes in life, etc). Others where the cost becomes far too expensive (they added more users than they could reasonably pay for), or ones that just didn’t get the business costs right (they thought that they could do 25k users and just run it on donations). There are probably plenty of other reasons too.