That's all well and good in theory, but in practice it isn't as easy.
Communities here will naturally centralize to the biggest ones. If all of a sudden an admin of the instance that a certain massive community is on goes bananas and starts de-federating from all sorts of instances and makes stupid decisions, just saying "hurr durr just go and make your own instance and community" isn't helpful because 99% of the people there won't just pick up and start again on a different instance.
The decentralized nature was supposed to solve the problems with centralization, but really all it does is make the same centralization problems happen more often.
That's all well and good in theory, but in practice it isn't as easy.
Communities here will naturally centralize to the biggest ones. If all of a sudden an admin of the instance that a certain massive community is on goes bananas and starts de-federating from all sorts of instances and makes stupid decisions, just saying "hurr durr just go and make your own instance and community" isn't helpful because 99% of the people there won't just pick up and start again on a different instance.
The decentralized nature was supposed to solve the problems with centralization, but really all it does is make the same centralization problems happen more often.