You could look at this like private citizens trying to block access to public lands (beaches) in order to make them de facto private.

Federated apps are trying to establish a commons, right? If Google can block access, then there is no commons. If the government can force easements on private land owners, I suspect the EFF could make a case for the same for App stores.

Nobody would be making Google host the Commons, just access. This is a much simpler case IMO than forcing Twitter or Facebook to carry messages they don’t want.