Clearly, not going for mass appeal. They are targeting a market that they think they can make the most inroads.

Just off top of my head, here are the top energy drinks and their demo's. Of course, this doesn't mean people don't cross buy or only drink one. I've had Pepsi, but Coke is my choice, when I drink soda.

Red Bull = Action sports
Monster = Rockers
Rockstar = Clubbers
Full Throttle = UFC, rocker, etc..etc... you get the point.

Hip hop urban market? There's the gap you need to fill.