Why do horrors movie fail?

I mean in every horror movie i watch there is never any realism.Either people start to have morals at the worst possible times claiming they can't just escape leaving susan to her demise because they've fallen in love or they need to find a cure for teds affliction instead of blowing his head off before it gets out of hand and when their in a haunted house why is the only possible escape everybodys comfortable with is the door? Why does no one ever make a running flying tackle for that window?