It’s a lot more legally dubious for them if you defederate. If your instance willingly connects and shares data out of their own volition, it’s like that instance giving permission. If an instance blocks communication via the ActivityPub protocol outright, what are the legal grounds for Meta/Facebook to be able to freely access that information? Even if it’s posted publicly to view.
As an example. I can have my own website and post some info there, write articles, have contact information. People can view it. Companies can index this information and make it available to search. But I’m guessing it’s not legal (or at least less so) to be collecting that information to process and sell. Companies can do that so easily because you agree to it in their terms of service.