I don't know, in the mid to late 90s I was a child on BBS, and a lot of those were semi-anonymous. Perhaps it was just scale, for that. A couple hundred to a few thousand people at most seemed enough, but also mods did work. I guess there was a certain amount of effort to get going, and maybe that was also a gate. Even the speeds, perhaps, acted as a filter.

Semi-anon yes, but also often with real world fet togethers.

It wasn't that anonymous. A lot of people were posting from work accounts with full email and other contact info.