If you really want something legitimate to blame the loss of hunting ground on, blame the Estate Tax.
Unless the heirs of a large tract are independently wealthy [meaning outside of the land holdings], their Estate Tax liability will likely force them to sell out. So, they hire a realtor to sell it. Maybe Cabela's - maybe not - big ranch brokers are a dime a dozen.
Farmer's and rancher's ET liabilities are, and have been, rising, due to the increasing value of their land. The rise in their land values is primarily because undeveloped land is now being priced solely on its recreational value, not its agricultural value. And, as is correctly pointed out above, there are more people than ever who are interested in recreational properties.
The problem is when a large piece of land whose owner has allowed public hunting access passes to an owner who either locks it up and shuts out the public
That's why we live in the US - if you buy something, you can do what you want to with it. When you bought your house, did you expect the previous owners to show up and sleepover whenever they felt like it?
The potential good news is the new 'recreational' owners are probably more likely to make improvements geared towards wildlife.
Montanans don't want our state to become Texas
Wildlife is flourishing in TX, because the people who own the land are working very hard to insure that it does.
Unlike TX, a large percentage of MT is owned by the state and federal government. Perhaps these owners aren't working quite so hard for the benefit of wildlife?