From a real-world perspective, a hero falling from grace is good ratings. Look at how much attention Lance Armstrong got after the doping scandal. Not that he is a great example of a hero, but people eat scandal up with a spoon. However, from a fictional perspective, people prefer the good guy to win at the end. Very rarely will a story about a hero that falls become popular in the mainstream. It has happened, but there is a reason Hollywood operates off of a template for their blockbusters; because that hero story hits all the right marks in our brains.