A small, old time discussion forum for a specific interest in my (rather small) language had only perhaps a hundred active participants and another few hundred casual posters. In that sort of environment it is actually possible for the actives to get to know each other and have occasional live meetings, which builds a much better community. The threshold of participation is a lot higher since a new participant would first have to find the forum and then go through the registration process, both of which filter out people who were not actually that interested in the topic.
In Reddit or Facebook, any "community" (the word in quotations because I don't think they actually are very communal) for even a mildly popular topic gets filled with thousands and thousands of posts from thousands or millions of casual participants. The quality of the posts get very low, it becomes impossible for anyone to read all of them and personalities of the participants don't matter at all.