This is like inviting the Catholic church in an institution specifically built to protect former victims of same and similar institutions.
Given that anyone can start an instance and federate with Threads, or join an instance that does, freedom of choice is unaffected.
Maybe some of that but my sense is that given how prescient FB has been on buying companies that grew to become staples, like WhatsApp and Instagram I would say what they’re seeing here is something like the future of social media - even if tiny.
Unfortunately they can’t buy it, but they can do the next best thing: position themselves to take advantage of it, while in its infancy, and if possible control it while they can still throw their weight about before it takes off independently.