Well, the big issue here is that we sort of don't have the power you think we do.
What I mean is, say you have 10 servers. 7 are Lemmy, 3 are kbin. Great, each admin has control over those servers. Then you have Meta. They'll run 1 huge server. When the 10 other servers enable Federation, Meta now has 10 servers of content that isn't even on their own platform that they can sell. Your data will literally exist on the Meta server because your data is not contained within your instance/platform once it's Federated. Meta can then harvest the entire Fediverse for data like this. It's like an absolute wet dream for them. They don't even have to coax people to use their own platform!
Meta must be defederated the second they so much as dip a toe into the Fediverse or everything you've ever done, or do, on any ActivityHub platform will be scooped up and sold.
Edit: And it's even worse because all it takes is 1 server to Federate with Meta. If server A is Federated with your sever B, Meta can sill pull your data from server A they Federated with, even if your local server B has Defederated with Meta. This is a huge problem.