Basically, it's money. The DDP was the original, and most common plan that was sold, by not offering the extras with the common plan, those diners would either upgrade or purchase a mug on their own.
For 2012, it seems that the testing going on at AS Sports (I've made the mistake to completely "letterize" that one too many times ><) may have an effect. Plus with the large upswing in plan costs, it's easier for them to include the mug now.