Actually, in Baltimore the rock station, WIYY, seems to do quite well at 5.4. A Classic rocker pulls a 4.2. But that's including the entire metro radio market.
I'm surprised rock radio does as well as it does nationwide. The music itself isn't as popular as it was two decades ago, but apparently it still has an audience.
Its fall from mainstream popularity didn't really get rolling until the '90s, so it's still in the comfort zone of many listeners (largely white and suburban) 40 and older.