As if Meta could give a flying fart about activitypub as competition. They could not care any less if someone gave them money to care less.
I feel fairly confident in saying that the only reason they're integrating federation is so that it won't work because we all defederate them, this is beneficial to them because it means we cannot talk family members and friends onto Mastodon, they want to connect to their friends being on Threads. However, this pre-empts any EU legislation forcing them to be interoperable. They are, "can't help it if the other side is not interoperating despite having the ability to do so".