Stereotypically speaking, Active Rock's core audience is usually working class white males, oftentimes without a higher education. In places like L.A. or New York Active Rock is mainly big with males 20 and under...
Hip Hop, on the other hand, thrives in multi-ethnic cities with both males and females 12-34 year olds. Big with both the working and the middle classes.
Modern Rock radio stations tend to have much better demos than Active Rock: middle and upper classes, big with 20-30 year olds, more female friendly, more multi-ethnic friendly, and more higher-education friendly. That's why they bill so well in places like L.A.