I believe it is due to habitat loss and predation. Crop harvesting equipment is so efficient that very little feed or cover is left in the fields. Many farmers have converted areas that once offered good winter cover (fence rows, etc.) into tillable acreage. I’m not blaming farmers as they are just trying to make a living, Low fur prices have driven all but the most hardcore out of trapping. Red fox and coyote pelts are selling for $14 and $30, respectively. I recall selling winter fox pelts for $75 in the 70s. Rising raptor populations are also a significant factor.