Only creator Cliffy B knows for sure, and he's not talking. Well, he is talking... he's just not saying much.
The Xbox's biggest shooter and, arguably, biggest game period of 2011 was supposed to be shown off at the Video Game Awards on Spike the other day but was pulled at the last minute. The big mystery, just why it wasn't shown off, was sort of explained by Cliff Bleszinski as he spoke to 1up during the actual show.
Not really explaining anything, Bleszinski simply stated that pulling the trailer was a strategic decision. A statement that I suppose translates into 'we didn't want to get overshadowed by anything'.
Watch the interview here.