I still use a few forums, but what lured me away from some of them years ago was the fact that either reddit or Facebook had groups about everything in one place, and without all of the spam that the forums were starting to suffer from. Same with usenet. Groups are great but the spam was relentless and difficult to filter out after a while.

after some very negative experiences with reddit as a whole, I barely use it and now seek out dedicated forums. Same with Facebook. I no longer feel that the single sign on world has the benefit that it used to.