This is... fairly normal; possibly people forget because we have been in a period of relative stability for social networks, but this is how it usually works. It's basically how web forums reproduced, when those were the primary form of social media; forum starts to get a bit shit, people get annoyed, communities within that forum start decamping en masse for elsewhere (often a completely new forum). It's a fairly natural human behaviour; if the people you interact with go to X, you probably go to X, too.

I mean, what do you expect to happen? 20% to Mastodon, 20% to Threads, 20% to T2, 20% to Bluesky, 20% stay, to avoid being perceived as a 'hivemind'?

This is actually one reason I think it's rather unlikely that there will be a single Twitter-killer, with everyone from Twitter moving to Threads or whatever and then continuing on as normal. Threads will probably be the biggest (particularly if it manages to launch in the EU; that's a big problem for it right now), but I'd expect a year from now that there'll be Threads, a bunch of Mastodon instances (maybe more loosely federated than today, probably more community-oriented), maybe Bluesky (I don't personally _get_ it, but some people seem to like it) and a rump Twitter.

Many had automation that broke with the twitter api being rug pulled.

Others don't care for the way they systematically dismantled their trust and safety team.

And finally, some just don't like the direction the platform is heading.

Twitter has made it clear they don't care about their employees, their platform users or anything but frantically trying to extract a bit of money out of zombie company.

The tech community in general but especially the infosec community has strong representation from the LGBTQ community. It should be no surprise that Musk’s antics would drive that community off the site before others. The fact that they are more technically competent than other Twitter sub-communities (like sports or movies) means that the initial learning curve of Mastodon was not a blocker.

If most the infosec professionals consider the latest changes have made Twitter an inviable option, that alone speaks volumes of the quality of those changes.

Also, a highly changing environment (regarding security threats) makes strong networking a survival trait. You don't want to become isolated from a part of the community, and you can always keep both Twitter and Mastodon. In fact, keeping both accounts is a must, because many security companies and government institutions are still only on Twiller.

Yes, that's how communities work.