Music

Comics are a medium that don't really lend themselves to music.
There's no sound.
You can draw some random music notes around a dialogue balloon with song lyrics in it, but it's not the same.
Maybe that explains why there weren't a whole lot of ads for music in comic books.
But, the marketing reps probably figured that people that read comic books probably also listen to music at some point in their lives, so it was worth trying out an ad every now and then.