Christopher Booker in The Seven Basic Plots:
Each [plot] begins by showing us a hero or heroine who is in some way incomplete, who then encounters the dark power…the essence of the action is that it shows us the light and dark forces gradually constellating to produce a final decisive confrontation. As a result, in any story which reaches complete resolution…the ending shows us how the dark power can be overthrown, with the light ending triumphant. The only question is whether the central figure is identified with the light, in which case he or she ends up liberated and whole; or whether they have fallen irrevocably into the grip of darkness, in which case they are destroyed.
Booker explains how this urge toward light and wholeness is why we tell stories in the first place: not as entertainment, or escape, or even to simply make sense of the world. They are devices to lead us toward wholeness and light.
His analysis is fascinating, despite my personal reservations with identifying one reason for an occurrence. I know of few phenomenons caused by one factor, and many caused by a multitude. Yet, a Jungian analysis of stories and how they entice and urge us toward wholeness shows their psychological power — why we feast on them, whether through movies or television or books, or the story of a sports team or player, or simply the story a friend is telling — and how conservative they ultimately are. The bad guy loses, the good guy wins, and the morals of compassion or learning disciplined strength are endemic. That is, they are not morals in a Three Little Pigs sense, but we simply don’t experience many stories at all where the bad guy wins, or where the hero or heroine doesn’t show compassion. Stories are moral devices even in the 21st century.