This isn't a problem that is limited to the USA.
I live in New Zealand and have a workshop on the local airfield.
Of the 9 hangars at the airfield, only two now have airworthy aircraft in them -- and most of those are home-built or microlite types rather than GA craft (like Cessnas).
Just about the only (semi) regular users of the runway are flight schools which train pilots for overseas airlines such as EasyJeet and JetStar.
The skyrocketing cost of maintaining a PPL combined with hikes in just about every other cost associated with flying has really seen the amount of activity plummet.
Even the local CAA (our equivalent of the FAA) field officer told me he's not going to renew his pilot's license because of the costs.
On the up-side.... the whole issue of drones being integrated into the national airspace may soon be made a lot easier -- since there'll be far fewer full-sized craft in that airspace anyway