Let's see, some people might hate them because it's mainstream, some people might hate them because they're not interested in them, but some friend/relative/random guy on the street can't shut up about them.
And then there's the people who played them, found them boring, and therefore "dislike" them. Many of these people tend to say they don't like the game if asked, but they don't go around preaching about how bad it is. Unfortunately, even though I think the majority of people fall within this group, it's the vocal minority who are in the spotlight most of the time.
But remember, even if someone say they don't dislike a certain game, that doesn't mean they automaticly hate that game because it's popular. I get a bit angry when people say that I dislike "game-x" just because it's popular. Yep, it has happened.