Basically it's a reaction to the marketing hype machine in every movie studio. We're given expectations that a movie will be extraordinary through relentless marketing campaigns, but more often than not, the movie is a disappointment -- often because more attention is given to the production and post-production quality and not to the writing or acting. But we now live in an age were editing technology is relatively cheap and easy to use, and those with enough desire (or perhaps too much time on our hands) are trying to find the good films that were promised to us in trailers, magazine articles, press junkets and whatever else the spin machines have foisted upon us.
Notice there isn't a big interest in re-edits for Spider-Man or Lord of the Rings or even the new Batman movie. Good films aren't being screwed around with. In the case of Star Wars, the desire to do these projects comes from a desire to make the whole saga good again, especially when the OT is being screwed up and brought down to the level of the prequels. That's also why O-OT preservation is so very, very important.
Of course, a lot of what I personally do is create Extended Editions. Instead of trimming stuff out, I love to put it all back in, to see as much of movies that I am NOT disappointed in as possible. I don't have to create an Alien or Abyss or Gladiator or Lord of the Rings Extended Edition because the directors have been smart enough to recognize the demand is there. For the rest, it should be a lesson that a LOT of people tend to like the extended editions of films, even if they like the original theatrical presentation preserved. Spielberg realized this with the DVD of E.T. and we received a choice wrapped up in the same package. THAT is how it should be. The studios can either make money from the demand, or watch guys like us fill the demand ourselves.
It's our time vs. their dime.