Adam Mosseri:
Second, threads posted by me and a few members of the Threads team will be available on other fediverse platforms like Mastodon starting this week. This test is a small but meaningful step towards making Threads interoperable with other apps using ActivityPub — we’re committed to doing this so that people can find community and engage with the content most relevant to them, no matter what app they use.
Look at the fediverse’s monthly active users, it’s declining. There’s a pretty solid wall of friction when trying to participate and the vast majority of people won’t ever be a part of it in its current state. There’s no upward tend here and I doubt that it’s ever going to be a real danger for meta.