because Black Ops is more about just trying to act so hardcore, amazing, and such a pro that the main character, out of some miracle, is able to survive so many deadly hits when everyone else around him dies from them and then be saved by, once again, some elite army dude. No one really cares about anything else. Its kind of hard to do multiple live action trailers when they would all be the same thing - boom, bullets, rocket overhead, dude screaming on the radio, and then the slow entry of the game's title.