As soon as the aggregate of hunters learns to properly age deer on the hoof, the deer population will be much better off. The 13 inch rule creates an inverse to the desired effect of increased deer size (antlers) over time.
Short example: In the event a 2 1/2 year old deer grows a desired larger rack (14"+), he is eligible to be killed, instead of giving him the opportunity to breed a d create more just like him. On the other hand, the inferior 12" buck of the same age, gets to breed and live another season,... creating the opposite effect of making the deer population better.
If all hunters could age deer, however, then you impose a "must be 4 1/2+ years old" law. Then, you could selectively give the better bucks a chance to breed and make the whole herd better.
An over-simplified deer management rule is: Shoot the inferior deer while they are young and let the superior deer die of old age.