I think the decline started when the military pulled back support for highpower rifle competition type shooting. The Army had a whole structure that supported service rifle competition. Now it's pretty much the domain of the AMU only (more for glory and recruiting than for training for battlefield effectiveness). The USMC was the last bastion of riflemen, and they have adapted their course of fire to match the needs of their combat mission. They still run the Competition in Arms Program (CIAP), but Marines shoot a combat style instead.
On the civilian front, I see the younger generation enamored with the run and gun type disciplines. Those that do shoot rifles for accuracy, are picking F-class, or PRS. Easier to pick up and do decently than learning the highpower position (more instant gratification.).
