Genetics shot out. I doubt it.
Habitat. Very little change since the 80's and most of the changes have should be positive for deer.
Deer numbers are improving since the tough winter a few years ago but most of the gains have been on private and public numbers are lagging. This winter is likely to knock deer numbers back down again.
The biggest factor is hunters. Today there are more hunters and they are more efficient. This will be my 40th year of hunting hunting SE Montana. Back when I started there were few if any ATV's, rangefinders, GPS and all the other gadgets that help us be successful. A good rain or snow would make a lot of places inaccessible an a 400 yard shot was a long way and few hunters could constantly make shots that far in the the field.
Back in the 80's I seldom saw boot tracks in the road less places and now those places draw good hunters like a moth to a light. When I was young you rarely saw hunters from west of Billings. Now you see hunters with one, five and six licence plates all the time and even some with four and seven plates. My bet is that most of those hunters coming that far are not beer drinking road hunters but hunters that get after it. Says something about the quality of hunting in the western part of the state.
Another factor is the elk and it is not just the elk but the increase in hunters they bring.