I don't think their rivers are inherently more productive. I know that in some Idaho streams researchers added salt to the water to electrofish. The Idaho Batholith is pretty non-productive; it takes the fish quite a while to grow to fishing size. But you are so right that their agencies recognize who pays the bills and manages in that direction.

I do recall a conversation I had with boss when I was mentioning that the (then listed Bald Eagle) depended on salmon carcasses and that Hawaii had just lost a court case where depriving a listed species of food was a "take" under ESA that he would never manage salmon for eagles. This was in the 80s and I am fairly certain nothing has changed.