Board Thread:Questions and Answers/@comment-67.1.246.12-20130810173702/@comment-4913740-20140629144008

The GZ thing was primarily due to showing off The Phantom Pain as a different game, and ultimately splitting them in the end. Trailers always show off the beginning of a game and the origins of the story can usually be determined from them. By splitting the two games, they had to spoil Ground Zeroes in order to establish what the deal with The Phantom Pain is.

Hopefully, Kojima will keep The Phantom Pain mysterious still, and allow us to actually experience the story and not know all the details going in (although we do know the fact that Big Boss will end up becoming the antagonist).