In my opinion it's definitely the fact that they are over-hyped and get too much media attention, and the annoying craze over them by several teenage girls.
I don't like their music, but I can't say it's the worst on the radio. There's definitely worse out there. But the fact that there's always so much hype and attention from the media about them, is very annoying. There are much better artists who deserve at least some level of recognition and respect.