Comment by Kosirich

The trailer is a deliberate choice of the authors on what content to put in order to sell the game and present "the idea of the game". Not only that, but a lot of trailers are in form of a presentation with audio or text (more common) by the authors, where they deliberately emphasize what they think are strong points of the game. So in fact trailers, even very short ones, can tell a lot more than it's immediately obvious.