There have been a number of reasons for the decline of prairie grouse and even more, pheasants.
With PG there seems to be a trend of decline over a big area. The Dakotas and especially Montana have been a gradual decline for a couple years. My friend told me Montana was bad where he hunted this year. There are areas that are still really good but overall it's been in a decline.
Pheasants haven't had good conditions for several years! We had hail and not just a couple stones but storms where it hails for 30 minutes, torrential rains and floods during nesting and then drought, the winter of 22-23 we had lots of snow and really cold weather. Birds in South Dakota survive this but the difference is habitat!
Farmers farm fence line to fence line and road ditch to road ditch. CPR was taken out for crop production. Farming today is much cleaner than years before because of herbicides and combines are better and don't leave as much in the field. There is not much of an area for them to hide, nest, and survive in and predators numbers are huge! When you see a coyote almost everyday when out and about you know there are a bunch around!
I'm not knocking the farmer, they are trying to make a living in a tough occupation.
Overall it just a combination of things and just plain bad luck. Hopefully this year will be better.