Or people are getting older and they have to get on with their lives instead of sitting around and playing wow all day. Most of those people are planning on, or already have families.
I feel that if they would actually go the path that the community wants with the "lore", then I think that they can easily come back, so many people want to have some sort of expac based around the other side of the planet and to have more lore about the old gods, fuck if they did something like that I would be ecstatic.