We all can have our pet theories about why game bird numbers are down. The one I put the most stock in is decline due to lack of habitat. Too many areas are being managed both farm and woods as a mono crop system. Entire farms one or two crops, entire blocks of woodland being converted from a mixed species of trees to all one or at most two types. Worse they cut large blocks all at once instead of multiple smaller blocks in a yearly rotation. It's feast or famine from the birds viewpoint. No cutover for a decade then a hundred acres for a year or two to enjoy instead of smaller cutover areas every year in the same basic area.
I have little use for the Game Managment department in most states. They focus on deer and turkey instead of other small game. And as far as I am concerned deer are like rats and will breed and thrive without mans help. And turkeys are so far down on my list I'd get rid of them off my land in a heartbeat if I could. Two plagues that mostly expand in numbers in spite of state management efforts which they gleefully point to as their major successes.