Regulations have the biggest impact. Genetics and nutrition are important building blocks, but if you are over harvesting young deer, then you will not see the benefit of genetics and nutrition.
Back in the late 90's and 2000's, Wisconsin implemented a program called Ear A Buck (EAB). In many units, especially the southern 2/3's of the sate, we had doe populations that were out of balance with herd control goals. The problem was that the deer hunting culture for many hunters had developed into "you can't shoot does because you will destroy the herd" mindset.
The program required that hunters 1st shoot a doe before they would receive a buck tag. In the years it was implemented, Wis led in B&C entries, helped to reduce the doe population, and allowed for a better age structure to develop. It also appeased the car insurance folks as i believe we had some of our best harvest #'s during that time period. It was misapplied in the north as they did not have the same herd populations that the rest of the state had. Rather than the DNR making adjustments to the program, they simply cancelled it all together.