I don't know if it's deliberate, but I will agree that National and State Parks seem to be some the most expensive places to camp. Here in Colorado, a state park will charge you $7-$10 just to drive in the gate and a camping spot runs $15-$20 a night depending on services. They seem really geared towards the RV/Trailer camper. Forest Service campgrounds run $10 a night or less, but there's no electricity (which keeps my wife away). My favorite is still backpacking in designated "wilderness" areas - no mountain bikers bombing down the trail with you, no motorized traffic, and fire is the only other thing that may be restricted if it's dry. The only human noise left is air traffic (funny how much you notice it when there' nothing else) and snoring.
BTW - I have nothing against mountain bikers. I just appreciate not having to worry about trudging up a narrow trail and having to jump out of the way of them. Happened to me again this weekend in a city park close to the house.