Post-reddit/HN these types/format of forums are dead unless they at a minimum include some mechanism to minimize irrelevant content. This is achieved in reddit/HN by voting/nested comments. In twitter by re-tweets/likes and likewise for other modern discussion media.
The thing I really like about forums is that you can have long-standing threads that collect a conversation in one place vs. repeating the same conversation over and over on places like reddit. Build threads in particular, where you can see someone take a remodel or build from ideation to planning to execution/correction to completion are extremely rewarding and educational. Those don't exist on reddit, people have to build that off-site and just link to it.
While on reddit/HN you just click [—] and skip whole subtrees of comments you're not interested in.
You can walk through the series of these threads and get essentially a replay of history of this project.
Of course as increasing numbers of passive users joined the internet, upvote-driven sites became more popular. That doesn’t mean they’re better for actually posting on, though.
One of the goals of all this is to automate moderation as effectively as possible without impacting the social dynamics of the community. At some point manual moderation does not scale.
It can be both. In the dying days of several community forums I was on, I noticed the conversation got more and more centered around links people were finding on Reddit or Digg. That was my first inkling that the days of bulletin board style forums were numbered. These sites are like genetic algorithms for surfacing content people want to discuss. So even when they want to discuss it with closer people than the firehose of Reddit, they're bringing up the same links and content.
It's only a matter of time, though, before people prefer to just go to the source. And that kills the forum traffic.