The more users, the more diverse people you'll run into.

But I thought the article described it in the wrong way. Mastodon was down. Well one instance was down for the author because some big names had signed up on it.

The emphasis should be on it being decentralized. A modern day IRC where any community can run their own nodes and communicate with other nodes.

Running big communities is a challenge regardless of technology, just see Freenode for example.

I remember running IRC Networks back in the day, it required time, money and organisation. Sometimes even donations.