They didn't want to put too many of the ideas into it that we could save for a second one. So we could see what the appetite was, because the bigger movie would actually be what comes following that. That kind of sets up a new storyline, new location and world, and then you can really go crazy from there" he said.
God, that kind of thing is just infuriating to me. They had an opportunity to create a really GREAT movie here, with a lot of fresh and interesting new ideas... but decided to give us just a safe and predictable rehash of the first movie instead, while holding all the new stuff for the sequels.