Why is it usually the sweet, innocent, virgin girl who survives the horror film?

The one who says 'no' to the and drugs is usually the one who becomes the heroine and defeats the killer at the end. This same formula takes away the fun from slasher films in my opinion. If I were a director, I'd make it more realistic: The teenagers who are 'bad' survive while the 'goody two-shoes' die a horrible death because real life doesn't distinguish who deserves to die and who doesn't. It's all random.