There are a ton of reasons not to like it and they’re evident on Lemmy pretty notably, let alone other platforms. The entire idea of being able to defederate and federate at will is a big feature of these platforms but they’re also the part that people like the least. If the server you’re on defederates from another server you like, you have no choice but to start all the way from the beginning if you need to choose another instance to join. At the same time, each instance gets its own version of every single community. If you join an instance that federates with lots of other instances, you’re very likely to see the exact same posts multiple times since each community is completely unique and separate (again, a feature for some, a boon for others).

Federation is great for a few reasons and really horrible for others. It’s not the single answer that works for everyone.