The question is always: What's the alternative? People who are either addicted to what they get from Twitter, or whose job depends on it, have no other place to go. Of course there are other platforms, but those only have a tiny fraction of the user base, meaning less content and less attention.
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.
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.
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.
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.
