it's not because of politics or religion or anything similar as this is nothing against the law,
They also go down because of racist, bigoted, otherwise hateful content. They'd need to fund themselves because nobody is going to advertise on those sites. The site that I did join turned into a cesspool of that type of content pretty quickly once the Reddit refugees found it. You couldn't talk about anything without someone finding a way to use it to insult people of other races, specific races, etc... It also started to become a site full of misinformation pretty quickly. Eventually, it was innundated with 'QAnon' people.
I watched the spectacular downfall with popcorn, mild horror, and some philsopphical thoughts about human nature.
When I joined the site, it was 'free speech'. It just wasn't overrun by neo-nazis at that time. I was usually just disappointed with people, which isn't an unusual position for me to take. I felt sorry for their education, lack of experience, poor family upbringing, and things like that. (I'm only partially white, for the record.)
Ah well... That site is no more and I don't think there will be another like what it was when it first started. It was largely intellectually gifted people discussing everything from history to current events. Science and logic won debates, instead of lies and bluster. Once the tipping point was reached, it was an echochamber and all the original people (including the founder, as it was their college programming work) left.
They say the way to counter hate/racist speech is to speak against it. That's impossible to do without the numbers and desire to do so. It soon turned into almost nothing but that type of content. I say the change would be worth studying from a psychological position, to see where that tipping point was exactly.
Anyhow, we've not yet crossed the Rubicon, but we're nearing the point where the conversation could easily start containing content best said elsewhere. If you do reply, do take care when doing so. I've edited out a few comments in this response to you. It's all too easy to fly too close to the sun!