I think this is great. I've been using threads for 6 months, and while I was never a prolific twitter user - I thought it sucked even before the elon purchase, now, it's entirely unusable to me (and I've tried) - I do like its interface, a seemingly "light" (by meta standards) approach to moderation, and now a step in this direction I think is a really good thing.

As to the "why" I think it's fairly obvious. If they integrate with everything, they'll eventually become the defacto platform and/or steer users and engagement to their other platforms with less friction.