A lot of the audience fragmented for various reasons, and even within the same discipline, not everyone has converged in a new place yet. I'm told mastodon got more CS/phys science people, and Bluesky got more social scientists. That's a shifting landscape though.

There was one obvious place to look for these discussions; now there are many. Changes to search tools and API access didn't help discoverability either.

Some of the departures are for practical reasons: Twitter regularly changes the rules around logged-in viewing, direct links, and promotion/ordering of posts in ways that create friction for people trying to engage in public outreach. ("this method worked yesterday" should refer to the software, not the communication, thank you very much!)

Possibly something about the way women and blacks and jews and gays and trans people and other minorities are being regularly and systematically and reproducibly attacked and harassed by neo-nazis and MAGA trolls who Elon Musk retweets and supports instead of discourages and bans that turns academics off from Twitter/X.