I think this is just market fragmentation. Usenet's big advantage was that it was the only large-scale easy-to-access (nearly every ISP provided it, easier to get to than FidoNet) "social media" site in real use. Today there's a gazillion web fora. High-profile social networking sites appeared and then disappeared. You could have spent half your time just creating new accounts to keep up with whatever was popular. See, for example, the rise and fall of MySpace.

I guess most of the cool kids hang out on Facebook these days; I'm not bothering at this time.