As the OP is speaking of Arizona State Parks specifically...
This is their mission statement:
Managing and conserving Arizona's natural, cultural and recreational resources for the benefit of the people, both in our parks and through our partners.
If the campsites sit unoccupied, paid for or not, they are NOT for "the benefit of the people".
This argument that "as long as they get the money who cares" is only valid if were private property. It's not. It's government land held for all people to enjoy.