From my perspective as someone who wrote and moderated his own NIH forum in 2000 - still in use today - the main reasons for the slow decline in usage both by users and publishers were:
- the move to media-heavy content (images and video) and the problems integrating this seamlessly into discussion forums and moderating it (as a non Big Tech publisher)
- the increased politicisation of online discussions and more complex legislation regarding "hate speech", privacy etc., all of which make hosting and moderation of user-content platforms unattractive for all but the biggest publishers, so most moved to FB groups or similar platforms to reduce the effort required to moderate.
- non-threaded forums suck and threaded forums don't work well on mobile phones
- I suspect, but don't claim to know, that the bad quality of popular forum software and consequently many forums getting "owned" regularly with all dire consequences for users played some role in this.
- the move to media-heavy content (images and video) and the problems integrating this seamlessly into discussion forums and moderating it (as a non Big Tech publisher)
- the increased politicisation of online discussions and more complex legislation regarding "hate speech", privacy etc., all of which make hosting and moderation of user-content platforms unattractive for all but the biggest publishers, so most moved to FB groups or similar platforms to reduce the effort required to moderate.
- non-threaded forums suck and threaded forums don't work well on mobile phones
- I suspect, but don't claim to know, that the bad quality of popular forum software and consequently many forums getting "owned" regularly with all dire consequences for users played some role in this.