The reason is because elk are more pronounced during the rut, and fewer in numbers, from what I remember. Ultimately, if you look at the FWP plan, it's because deer hunting is managed for hunter opportunity first, and is likely regarded as a resource that is abundant and in good stead, until there's a disease issue or the herd is below the metric set out in the plan. So part of it is biology, and part of it is "folks like it."
This is a better way to frame this. MT hunters love that opportunity, and for the longest time, defending 11 weeks was critical to ensure public support for hunting. Now, as the world changes, there is a desire to change management philosophies in a state that lives & dies by how many days afield you have each year chasing big game.