I think it's best to see Twitter as a network of networks. Some of those networks have moved (or at least lost enough members to Mastodon/Tumblr/wherever that the network effects are no longer strong for Twitter). Others not.

I'm an academic in computational political communication. I wasn't fond of Twitter before the move, but was there largely because my professional network was. Most or all of them are now on Mastodon, so the network effect driving me there has gone (and I've cheerfully left). My wife is an author, and book Twitter is mostly still there. Ditto the journalists.

I mean, my part of the job world was never on LinkedIn - while for others it was indispensable. This feels like the same.