User blog comment:H-Man Havoc/Brand new ME3 launch trailer!/@comment-76.171.184.23-20120303020109/@comment-1691295-20120304045419

Trailers almost never use music from the game/show/series itself.

ME2 used Heart of Courage by Two Steps From Hell, ME3's CG trailer used Black Blade, also from TSFH, the Femshep trailer used TSFH's Armada and this trailer is Protectors of the Earth.

Trailers don't use in-game music because no music from the game is made to tell an epic story in two minutes. There is just no place in the game were such music would be appropriate. Trailer music would also be incredibly overbearing in-game.