First off, David Koepp's script for Spider-Man was awful. It was a miracle that Raimi and his brothers, along with an uncredited Alvin Sargent, managed to edit it into something salvagable for the first film. Why don't you think he was brought back for screenplay duties for either sequel?
In general, David Koepp is one of the worst "blockbuster" screenwriters today. His films are largely dumb, poorly written pieces of trash. His name gives me no hope.
Also, George Lucas is a BUM.