I see what you’re saying, but I really don’t see what Meta stands to gain in the long run from an open fediverse. It just doesn’t seem compatible with their business model to allow users who aren’t on their platform to interact with content created on their platform. They need data so they can sell it to advertisers, and I don’t see how that works when your users can just jump to another instance with no advertisments and access all the same content.
What do you think Meta stands to gain from Activity Pub, and why wouldn’t they just make their own closed protocol? (I am asking in good faith, because I do not really know.)