I think it's also true that Twitter has copied it with Spaces in a very useful way. I see it sometimes after a big event, people who are there anyway start it to discuss what they experienced.
But people wrote off Snapchat a few years back too, and apparently they're not doing bad these days even though I don't know anybody using it. Maybe the number of people online is so large now that you don't need total domination anymore to be successful, especially if only a small part of the users are creators and the rest just tunes in.