The reason for the delay is actually quite simple. Developer Bluepoint, who is handling the Xbox 360 version, needs additional time to put the finishing touches on the game to ensure an awesome experience.
While this isn’t ideal, we would prefer that the developer take all of the time that it needs to get it right. Titanfall is the biggest release so far this year, and since the Xbox 360 version is expected to carry the sales load for this title, it is important that the conversion to the previous generation platform be the best that it can be.