John Bull wrote a post (in tweet-sized pieces, naturally) that rings true for me, and he gave a name for the phenomenon we're seeing with Twitter, saw with LiveJournal, and partially saw with Stack Overflow. The thread starts here on Twitter and here on Mastodon (the Fediverse). Selected quotes:

One of the things I occasionally get paid to do by companies/execs is to tell them why everything seemed to SUDDENLY go wrong, and subs/readers dropped like a stone. So, with everything going on at Twitter rn, time for a thread about the Trust Thermocline.

So: what's a thermocline?

Well large bodies of water are made of layers of differing temperatures. Like a layer cake. The top bit is where all the the waves happen and has a gradually decreasing temperature. Then SUDDENLY there's a point where it gets super-cold.

The Trust Thermocline is something that, over (many) years of digital, I have seen both digital and regular content publishers hit time and time again. Despite warnings (at least when I've worked there). And it has a similar effect. You have lots of users then suddenly... nope. [...]

But with a lot of CONTENT products (inc social media) that's not actually how it works. Because it doesn't account for sunk-cost lock-in.

Users and readers will stick to what they know, and use, well beyond the point where they START to lose trust in it. And you won't see that.

But they'll only MOVE when they hit the Trust Thermocline. The point where their lack of trust in the product to meet their needs, and the emotional investment they'd made in it, have finally been outweighed by the physical and emotional effort required to abandon it. [...]

Virtually the only way to avoid catastrophic drop-off from breaching the Trust Thermocline is NOT TO BREACH IT.

I can count on one hand the times I've witnessed a company come back from it. And even they never reached previous heights.