I think that's a question of accessibility and time investment.... maybe there are other types of games that are able to capture the social experience even more. I would also just observe that as World of Warcraft evolved over the years, it actually kind of became less social, because in an effort to achieve more accessibility, we kind of removed some of the reasons why you need to play with the same group of people over and over.
I think that it takes away some of the reasons for some people of why they play, and why they might want to continue to play.
