Hardcore is a prime example of what I'm talking about. HC is for mature players (granted an immature portion of the community still journeys there). Core is where all the little kids are mostly and where the mature players tend to skip because they dont want to play against QSers and spammers.
Also note that I mention immature and little kids in different breathes. While they tend to be the same I think at the same time you they are different groups. Little kids can be mature just as much as adults can be immature.