I think this stems from our need for movies to have happy endings, for good characters to be redeemed and for bad characters to be punished. We seek out movie entertainment for things to go "right," unlike our lives where things happen that aren't always fair.
It can be argued that entertainment should just entertain and make us feel good, but I admire a story where filmmakers don't feel the need to wrap everything up in a neat little bow before the credits. Some people live happily ever after, others sadly don't.
Should movies have happy endings?