I don't know why people just can't use plain old forums. I've got a lot help from KVR (a forum for music making) since I started learning DAW. It works fine. If authentication is a problem then just let users login with their discord/twitter/reddit accounts? Is it the lacking of "one-click setup" forum services?
They all have the same issue of a Network effect[1] to overcome. Sure, I can whip up or take over a dead forum today and dictate the direction, but I will likely struggle to get a dozen users in a month, let alone a dozen comments. Meanwhile, there are probably 12 new sign ups for reddit as I type this message.
There's dozens of reasons why this is hard to overcome, but to put it bluntly: people don't leave if they are comfortable with what they got. if Reddit works for someone, why search out for some forum that doesn't show up on search to find maybe 12 comments abut something, when reddit has hundreds of posts to read? Users are metaphorically lazy, and the biggest sites feed into that.
[1]: https://www.forbes.com/sites/forbesbusinesscouncil/2022/10/1...