I'd say a big factor is the lack of ability to just socialise. Forums, even those built around some specific topic, normally had a busy "offtopic" section for g

I'd say a big factor is the lack of ability to just socialise. Forums, even those built around some specific topic, normally had a busy "offtopic" section for general chatter. Here, everything has to be at least vaguely about the subject of the thing being linked to, with no space to talk about how your day was or whether you liked <movie> or what have you.