In my opinion, the people that use Instagram and will potentially use Threads aren't the ones who will get into the Fediverse.
They will probably not even know that this exists in the app as it just puts you directly in threads.net.
Also, there's the option that this is just a 'trend thing' that will die in a week or two, probably because people won't get used to or due to legal problems (as it's already happening).
Edit: typo.
And now I feel the urge to reply to this comment.