I think it is about winter range. Thousands of mule deer used to winter on the lowlands in the Boulder and Paradise valleys. Many of these came from the park. Today it is dozens. Many hundreds of elk on what used to be the low winter range today. Big herds of elk laying behind Arrowhead school in the Pray area of Paradise valley and other areas in the winter now. There were zero elk on the valley floor in the 1990s, they didn't even fence the haystacks.
The area around Daley Lake/Dome Mountain refuge used to crawl with mule deer in the winter. Today the elk try to stay on the valley floor even when they shoot cows in the late season, they move off but will not go over the hill.
Fridley creek, 8 mile creek, North Dry creek, Bullis creek, Antelope Butte, Bullis creek, all had hundreds of mule deer wintering on them back then. Today... hundreds of elk and a few dozen mule deer.
For years I thought it was predators and predators definitely have changed the areas that elk use. Recently I have been hunting an area that used to be very good Mule deer country but now has very few. It has a large elk herd. Surprisingly to me there are quite a few Whitetails, even up to 7000 feet, though I have seen zero mule deer in 6 days so far. I can't see predators killing all of the mule deer but not Whitetails.
Anyway, some day we will have a study, or Wyoming will, that sheds some light on the situation. Meanwhile, anyone with a memory of what used to be around here creeps closer to ageing out. Regions 6 and 7 are going to have to pick up the slack. Lol