No, it’s not obvious that conversations would be controlled by it’s participants when there are hundreds or thousands of participants.

It works fine for 5 people, or even 10, but not once it scales beyond a certain point.

Just like having a voice call with 5 or 10 people can work, but with 1000 people you have to force mute everyone or it’s going to be a shit show.

The admin keeps the server running.

As for moderation, it’s far more time efficient for a small group of people to handle this than it is to leave it up to individual users.

If one person posts a spam message, it’s easier for a couple people to report it and a moderator to remove the post/user than it is to have a thousand people have to see it and decide if they want to ignore/block it.

Yes, unfortunately

I’ve never seen such a thing.

I usually just read the Wikipedia article, and then check the sources at the bottom to dive a little deeper but they usually aren’t books.