Long story short: they offer better sound quality thanks to the larger drivers. Seriously, earbuds just can't compete with over the ear cans on sound quality. They've gotten much better than they used to be, especially with the proliferation of canalphones, but then headphone technology is constantly advancing as well. As for why Beats by Dre and Skullcandy are the two main brands you see: it's the same reason most people who buy home theater systems either have or want to have a Bose system -- marketing. They're mid-fi products that sell at hi-fi prices, but they look cool and they have this aura of being hi-fi, even though they really aren't. Granted, mid-fi is still pretty darned good compared to what most people are used to, so they're not bad if you can get them for a fair price. I have a pair of Skullcandy earbuds myself, but if I were to get a pair of over the ear cans (I used to have a pair, but it broke after years of use and I never replaced it), I'd aim for something like KLH, Koss, Senheiser, basically brands that spend more money on engineering than marketing, and give you a lot more bang for your buck.