Counter anecdote: the last traditional forum that I have any interaction with was so plagued by spam that they turned off registration and the new registration system is “send an email to the admin asking for an account”. Needless to say, they aren’t a growing community anymore. They also don’t use SSL because none of their admins are fluent enough to set up LetsEncrypt. Don’t forget that lots of non-technical or less-technical people like to have forums too.