I can visualize an arrow, either when it is under load from the bowstring, or when the tip encounters resistance; wanting to bend under force. In the case of the arrow's tip entering an animal, the back of the arrow will want to try to overtake the tip if the weight is distributed more to the rear. So the arrow will bend or yaw and cause a loss of penetration. Having more of the arrow's weight distributed towards the front of arrow will cause it to be more prone to pushing straight through the animal. Makes sense to me.