I totally agree, and I believe that was also the reason why IRC was so successful in F/OSS communities.
Traditional thread-based forums are great for archival but also seem to encourage a full-sized post, which is a conversational barrier by itself and also limits the potential engagement by reducing the number of people willing to reply. It doesn't seem to me that the discouragement of short posts is inherent to forums though, for example traditional South Korean forums had been traditionally evolved from BBS and had a strong dichitomy between posts and comments, so short comments and quick reactions were norms (longer replies are typically posted separately in a post). GitHub issues seem to be somewhere between those different models.
Traditional thread-based forums are great for archival but also seem to encourage a full-sized post, which is a conversational barrier by itself and also limits the potential engagement by reducing the number of people willing to reply. It doesn't seem to me that the discouragement of short posts is inherent to forums though, for example traditional South Korean forums had been traditionally evolved from BBS and had a strong dichitomy between posts and comments, so short comments and quick reactions were norms (longer replies are typically posted separately in a post). GitHub issues seem to be somewhere between those different models.