What I think is Activision decided to gut it. If you look at the trailers from a year ago they showcase areas fully rendered in game that aren't in the game. They have shown a social hub in the Reef, Saturns rings in a cutscene of a ship traveling down to the planet, and a Forest like area. They also had said Mercury was to be in the game as a lush garden world. I think that Bungie was making something special and then Activision came in and said "what can we do to maximize profits?"