I believe that's a bit of a misleading meme that's making the rounds. You can deactivate it, which is functionally the same, and they haven't yet rolled out the feature to delete it because they rushed this thing to market to take advantage of Twitter's dumpster fire.

I also might be slow here, but I struggle to understand why this is a big deal. There are countless reasons why I would have reservations with Meta, but aww shit I can only deactivate not delete the Threads account associated with my source Instagram account seems like a weirdly esoteric hill to die on.