I personally believe that Meta never intended Threads to be support Activitypub and just chose it so they could do the bare minimum to comply with the EU digital markets act.
Honestly this is why the whole “Meta will kill the fediverse” thing people were saying never really convinced me. They just don’t seem to care, I mean it’s been a month and they still have no real plans to actually federate.
If they really wanted to they could already do that by setting up an instance and not publicly announcing it.