Why do sequels exist?  Sure in this modern day our generation needs to be bombarded with constant stimuli to even be bothered to pay attention.  We've become saturated in an age where so many parcels of our daily lives are conveyed to us through so easy a means that it takes little effort for us to become upset at anything we encounter that doesn't offer complete and instant gratification.  The idea of sequels I'm touching on here isn't exclusive to le cinéma, either, as our entertainment dollars constantly pick and chose through funded popularity what intellectual properties continue to exist.  Hollywood and even the video game industry have become obsessed and with and work tirelessly towards rehashing an already existing concept.
     With written stories or oral traditions, we see similar motifs and themes persisting throughout each medium: the fall of man, the story of creation, the great flood, the resurrection, they've existed in multitudes of cultures, the stories get updated to reflect modern ideas and cultural habits that persist in the time of each tale's reformation.  From the journey of the hero to the constantly repeated morals from fables and nursery-rhymes, the same story may be told, but the matter itself, the subjects, the locations, they all change to cater to a specific culture or time.  In the more modern sense of sequels of which I'm trying to lampoon, sequels serve no purpose outside entertainment value.  The powerful story involving the rise of a chosen one to triumph over the forces of evil with the help of a wise and sagely old wizard has been once told through King Arthur and his court, aided by Merlin, and again through Harry Potter and his needing to be brought up and taught how to grow into his heroic role, similar to Arthur's training.  In modern entertainment we produce sequels not as a spiritual reinterpretation of the previously existing story, but so we can spend more time with the specific characters we've grown to enjoy.  We don't create similar stories to recapture the compassion and wonder of the original, we carbon copy the first movie, changing little in terms of characters and overall plot.  The audience has grown to expect to see the same people from the first film in strikingly similar situations.  We, expecting entertainment, hold film studios to high expectations, and when they let a Bond Girl die, or when Indiana Jones gets married, it destroys our image of the characters, which as Northop Frye might agree, is what we need to get that true romantic experience of the movies: we need stock characters whose future actions are easy to discern through their simple dimensionality.
  We have been retelling the same few stories from era to era, but with the advent of modern movies and video games, all we expect from a well-told story is that it would be somehow insulting to the original work if we didn't somehow expand it.  No one is clamoring for a Lord of the Flies 2 or a prequel to The Importance of Being Earnest because we can respect the original for itself, without having this knee-jerk reaction to needing to spend more time in that fictional world.