Fediverse

I don't think that this is entirely true. Every instance has admins, communities have admins and moderators too. They define and enforce rules, make decisions and perform maintenance. It's not that different from centralized platforms with the exception that there's no common higher authority.

I'd use something that people are already familiar with: emails are the most common example. But maybe people could imagine a world, where users on Facebook could see posts and interact with people from Twitter and vice versa. Platforms are different, owners are different, but people in this hypothetical scenario could communicate with each other. That's much more relevant to modern world than emails and probably not that hard to imagine.

Fediverse is like that, but you can also pay $5 for a server and start your own Facebook.

Imagine a bunch of separate web forums each with their own management and policies. We have all used those. Now imagine that they are loosely connected to each other behind the scenes, so you can cross-post between them, if the admins are willing. That's not too hard to understand, imho.

There is occasional minor drama when there are cultural differences between two forums (say a leftwing vs a rightwing political forum) and the admins get upset and start interfering with the backend connectivity (defederating other instances) because they don't like what members of the other forum are saying. That drama is not an attractive feature of the fediverse, but rather the opposite. Anyway, I hope that helps.