Still a mystery to this day

Context

List of instances defederating from Threads, the Meta microblogging platform: https://fedipact.veganism.social/
At the moment, Threads have incomplete federation with Fediverse microblogging instances: https://fediversereport.com/last-week-in-fediverse-ep-86/
Another meme about Threads: https://feddit.uk/post/18194873
Threads does not currently federate with link aggregators (Lemmy, Piefed)
Threads could work with the microblogging part of Mbin

The main arguments for people to defederate are

“Embrace, extend, and extinguish” strategy: https://ploum.net/2023-06-23-how-to-kill-decentralised-networks.html
A potential federation with Threads (should Thread decide to implement it) would overwhelm Lemmy/Mbin/Piefed with millions of users (compared to the 40k monthly current active users), transforming those platforms into a threaded version of Facebook
Defederating preventively costs nothing