Friendster, Orkut, Google+, MySpace, Vine, Flickr, Friendfeed...they absolutely do.
If you thought of an exodus after investors meddled in, mentioning Digg v4 (to Reddit) would have been à propos https://en.wikipedia.org/wiki/Digg#Digg_v4
That's just the obverse of leaving isn't it? The site loses any momentum, becomes stagnant, and peters out, or in the case of Friendfeed, became ripe for acqui-hiring, then effectively spun down.
Orkut actually kept growing for a while, but in secondary markets (not just Brazil, but that was its biggest geo), until started to stagnate then decline.
Digg is a great example as well.
Due to the distributed nature of mastodon, you'd likely create or move into a "community" of your liking. Where you'll meet friends and like-minded people. A little happy bubble.
You'd think it's a utopia where people can finally leave behind the "hell" that is Twitter. Turns out they need the hell. They've become addicted to continuous outrage and their counter rage is what was holding the bubble together.
As it comes to media and social media, it seems to me it can't exist without rage, division and hate.
Imagine social media updates like this: "Had a pretty good day at work. Ran into my conservative neighbor, we shared a drink, and agreed to disagree on a few matters. To each their own I guess."
Or news channels and papers largely reporting on things going pretty well and reasonable, which is like 99% of reality.
Nobody would want to consume that, it's super boring. Not at all "engaging". Happiness sucks. Even our escape of reality, entertainment, largely consists of even more suffering. Imagine a movie where nothing traumatic happens to the characters. What is the point of even watching it?