I think it's more from marketing purposes and getting the timing right. For example, if AC13 kicks off their campaign focusing on Ashes, Big Ant can talk about Don Bradman. If AC13's campaign talks up licensing, Big Ant can talk about Cricket Academy, if AC13 goes on about Team Mode, Big Ant can counter it with Career Mode etc.
Cricket is a niche market and the success or failure of the games might end up with who was able to make the right sales pitch to the consumers and get them to buy their product. Big Ant needs to see what new features, if any, AC13 comes up with after reworking on the game for the last 4 months.
Maybe AC13 will not have any new feature other than changing the name to AC14, but Big Ant don't want to risk going out there and AC14 comes along marketing a new feature like "a new immersive captain's mode with dynamic fielding which puts you in Michael Clarke and Alastair Cook's shoes like never before". Even though we know that's nothing but automatic fielding where you select the field using a field editor and sit back, for a casual gamer that might be the selling point. Most probably Big Ant are waiting for that information to be disclosed so they can embark on their campaign and counter their competitor as best as they can. Plus they would also be keeping an eye on whether AC13 fails to meet its release deadline once again leaving the market open to DBC14.