I think the reason people drift away from general purpose forums is because the proportion of uninformed opinion increases to a level where it swamps out the interesting, informed view. There are a few contributors here whose posts are always well worth reading, but far too many others think they're an equal member of some online community and just as entitled to express their ill-formed thoughts. There's obviously very little correlation between verbosity, knowledge and being able to form a sensible opinion. That includes some who actually make their living in aviation.
Aviation forums start out as a discussion between pilots talking about something they're out doing in the real world. The most active ones end up overrun by people who use them as a substitute for a social life. If you need a sensible discussion about a topic, there are much better forums with a higher proportion of people who know what they're talking about against those who feel compelled to chip in with some rubbish which takes the thread off in a totally different direction.
The sad reality for the forum addicts is that there just isn't enough change happening in aviation to continually feed a 24 hour discussion. That doesn't seem to stop them trying though.