The problem with federating with Threads is that then anyone who wants to join the Fediverse will just join Threads (especially the people already using Instagram or Facebook), leaving the success or failure of the Fediverse in the hands of a company whose interest is to attract as many people as possible to its platform, not contribute as an even partner in a federation.

says who? and you could just replace threads with mastodon.social in your statement

Those that are on Threads are likely not even aware of the rest of the fediverse. I think that when they interact with us they will be. And when Meta decides it's time to start ads some people will think it's better over here. Also, some people won't like Threads using an algorithm on their feed.

From what I found, a lot of the people who join Threads, wouldn't have even looked into joining the Fediverse in the first place. If anything, Threads is bringing the concept of the Fediverse to more people and some of those people may find that Mastodon and the rest of the Fediverse could be what they prefer, especially if you can still talk with your family and friends on here.

Threads are stuck behind dealing with their investors as we can push the Fediverse with new updates all the time