I think almost everyone posting here has made valid points. It's a connected web of problems, each sharing some importance in the decline of hunting. But the fact that hunting is in decline can not be denied.
As I look across the road from my house right now, there are 8 new homes (and I live in a semi-rural area). Precisely upon the spots where 3 of these new homes sit, I've killed 2 deer, a handful of pheasants and countless rabbits. Never again.
For my money, habitat destruction is the leading factor in the overall decline of the sport. Ok, so I've lost some hunting areas, and I found others. But finding them -- and people willing to let you hunt their private property -- is getting harder and harder. Let's face it, hunting is fun, but hard work. The harder it is to find a place to hunt, the less likely someone is to invest the time and money in future hunts, or in introducing new hunters to the sport.
I try to do my part. I've introduced many people to hunting, including my children, and that's the only way we're going to perpetuate the sport. I have a real job, etc etc, but my passion is the outdoors. It's made me write magazine articles, books, trying hard just to tell others how great the sport of hunting is. The thought of a future generations not knowing the excitement of a deer or bird hunt, or watching ducks come into the decoys, is very sad.
But the future does look bleak.
Keep doing your part to keep hunting alive in this country.