I would guess that people who are addicted to it or whose job depends on it are not the majority of Twitter users.

I agree that even out of those groups, there are not a lot of people deleting accounts and moving to other places. But, my perception is that a lot of people are indeed spending much less time on Twitter. Twitter competitors are not only Mastodon or Threads. It is also YouTube, TikTok, Instagram, Netflix and alikes, advocacy for consuming less social media overall, etc.

A ton of people have moved to Threads from Meta which is the most direct competition.

Then there is of course Mastodon and the upcoming Bluesky.

Addictions can end. Make the experience unpleasant and people stop seeking it.

The userbase is the key to the entire platform. Any minority platform that has been created for small groups like Truth are just echo chambers of a single subculture. The wide range of individuals and subcultures on the Twitter platform is the whole reason people still use it.

It was my favourite social network, and I had multiple accounts. I used it slightly professionally, but wouldn't say my job depended on it. Months ago, I deleted as many tweets as I could without paying to deal with more, and stopped using it. I don't feel like I've missed it all that much. The engagement when active never felt that great, so that probably helped. I've never used Facebook either.

I do feel a bit like "what's the alternative"; I like being an active contributor rather than a passive consumer, so falling back to just reading scraps on the net makes me uneasy.

This is like asking “what’s the alternative to nicotine?” - it may sound trite, but basic health is the alternative. A replacement is not the answer. You just need to quit.