I though it was because it reminded them of eating a hot dog.
One of my law school roommates swore that it is due to an oral fixation. He had quite the case built. I was almost swayed by his argument. Then I remembered: it's just cuz they have to.
Looks, genre, talent aside. I have a hard time not liking someone who would dress in all red meat. It's safe to say that PETA will be at her next concert.