Yeah this is the whole benefit of decentralized servers. I also have an account on Beehaw and I agree with their decision. They have a really great culture they're trying to maintain there through a massive surge of new users and defederation is a tool they can use too protect that culture separate from the rest of the Lemmy network.
They're under no obligations to federated with any instances of any size.
Really looking forward to some better apps for Lemmy and kbin. Hopefully a lot of good app devs come over!