I don't think it was learning to be more moderate, I think niche communities were pervaded with new users, which in turn caused a shift in culture and therefore later developed into new moderation policy. It's also been heavily corporatized as well, there are far less distal independent entities being a "big deal" and more centralization. But I haven't studied the patterns extensively and this is just collective anecdotal assessments of the shifts experienced from 2004 to present.