That's where the sales are - the mainstream pop genres. I have friends who only listen to most of that garbage and even they will tell you that everything on the radio is overplayed and tedious. The mainstream has never been known for its soul or anything but at least they would get you something fresh now and then...these days it's three to five songs all day... on three separate stations - I mean it...my city has three Top 40 stations, yet has no Classical station, no Jazz station, and no Rap/Hip-Hop station. The only other stations are Rock, 80s/90s pop, and an Oldies Rock station. When you lack variety people get disinterested in music altogether. I can't be bothered to listen to the radio. Not one channel. If I'm not listening to the radio how am I being exposed?
Currently the only form of exposure is something like youtube. And it's virtual piracy to the point where there's nothing compelling a person to buy. And yes, it's bad quality, but most people either don't care or don't have a system even capable of showing them how bad the quality is. I'd bet the #1 and #2 sources of listening to music would be ipod earbuds and "came-in-the-box" desktop speakers. If you can't hear the difference between a CD and a youtube, why on earth would you pay for it? Heck, most people won't even actively pirate a higher quality rip!