…Same reason — we already had a social network. It was called Facebook.

You're not wrong. I suspect a large majority of Twit users also have FB (and probably IG) accounts.

IMO Twit is not so much networking as potential proximity to power. You can tweet at famous / powerful /interesting people (e.g. rock stars, politicians, authors/journalists) and maybe get a reply or a retweet.

That Threads is part of Meta means you can just slide over, keep your existing FB/IG network without having to pick a server (Mastodon) or learn a new interface (BlueSky). If those powerful/famous/interesting people decide to also have accounts there, then it serves the same purpose as Twit, minus the drama, minus the bad actors looking to 'own' you because you have a different view.

I'm not saying Twit will collapse, but it might be about to have a lot less influence. And as Musk ups the pain level for ordinary users, he might be actively pushing them towards Threads - if it ends up having similar network and proximity to power as Twit.

From a different angle, given that advertisers on Twit are potentially unhappy about their adverts appearing next to racist/misogynistic screeds, they’ll likely be happy to have a place protected from that kind of behavior. Musk claims to be a ‘free speech absolutist’ (his having censored people to the side). “Free speech” does not mean “speech without consequences”. For Musk, the consequence looks to be a hit to his bottom line.