I like the scroll view in discourse. Makes it super easy to follow a thread. The subthreads and replies are also easier to use. The search is better, the ability to upvote makes it better for some use cases, and in general phpbb is a mess in terms of actually being able to see what's useful and what threads are relevant.
I think flipping the question makes more sense, why do you think some forums switched to or started using discourse instead of just using phpbb? I can guarantee you that it's not just to follow a fad or whatever, most niche or support forums don't care about that.
I think flipping the question makes more sense, why do you think some forums switched to or started using discourse instead of just using phpbb? I can guarantee you that it's not just to follow a fad or whatever, most niche or support forums don't care about that.