Not every user is the same from a revenue perspective. I find Threads to be obnoxious because it's full of boring athletes and influencers, rather than interesting scientists and people writing sarcastic jokes. But (based on the advertising on network TV) I'm willing to accept the possibility that there might be more money in advertising to the kind of audience that likes athletes and influencers than in advertising to weirdos like me.
All it takes is for a solid chunk of the high-revenue "boring mainstream" audience to exit in order for Twitter to be permanently damaged as a revenue-generating enterprise, even if it still has lots of users. (And as a Twitter addict I think that would be sad! Not sure why the downvotes over a legitimate concern.)