As I've seen posted before, one of the reasons is due to enshittification. Feel free to peruse at your leisure. Greed is certainly the biggest contributing factor, but there's another, lesser talked about effect happening here that "compliments" enshittification if you will.
It's a sort of "reverse gentrification" of a social media platform that has just crested in popularity/usability, which in turn creates a snowball effect (or in the interest of the aforementioned process, a "shitball" effect). It's when the good posters, the ones that actually READ the articles, the ones that make educated or otherwise well thought out comments and actually take time to speak to the person behind the computer instead of using anonymity as a means to be vile or rude or nasty, all migrate off of the platform. They see the writing on the walls, and so they leave. This leaves behind more and more of those that don't really care about details or politics or social causes, nor care about anything other than their instant gratification (i.e. we don't care about the blackouts we just want everything to open back up so we can get back to our memes).
In other words, as more decent people leave a social media platform, all that's left are the ones that make the platform undesirable to begin with, thus causing more people to leave and the decline deepens. We saw this with Facebook. All that's left on Facebook are people who are out of touch with reality and those who use the platform as a propaganda machine.
We're also seeing a rise in what I can only describe as "Corporate Apologists" - People who constantly make excuses for companies that shouldn't be defended or are otherwise indefensible. It is pretty disheartening to see so many people rush to the side of businesses that are openly exploiting their workforce (in some cases the defenders are the exploited, which boggles the mind). People who defend Elon Musk and his handling of Twitter, people who defend Reddit and think the blackouts were always going to be useless so why bother (those people missed the point entirely), people who defend anti-union tactics or businesses that don't want their employees to have living wages. All of these are because the person has some self-image or interest that is tied to that business/platform. A part of (sometimes a large part of) their identity is defined by a product and so they won't even entertain the idea of trying to go against it, lest that product or company be taken away (and a part of their identity with it). There are people who really pride themselves on their number of followers, their internet karma, other useless tokens that they attribute to personal self-worth.
Anyway, I've ranted long enough. I'm tired so some of what I said probably doesn't make sense and I apologize. Maybe I'll come back later and clean it up a bit once I've rested.