As someone in the business doing Risk and Safety in State Parks I can say this was not an easy decision. Here in Virginia, the State has refused to heed any advice from people like myself who have advocated shutting down parks. So the counties, have made the decisions that Parks and National Forrests within their counties to enforce this stay at home within their control.
Lots of reasons for this move, but just a few:
1. Sanitation and Hygiene. People are pissing and pooping wherever and whenever. Inability to clean and sanitize appropriately. Overcrowded parks with no bathrooms equals a DEQ nightmare.
In the risk world, one might consider parks being open as open and obvious and partake at your own risk. This is fine on an individual bases and under traditional circumstances, for example mountain climbing. However, all it takes is one person to pass on to hundreds. This is not business as usual nor normal circumstances.
2. Personnel and resources to protect themselves and the public are limited. Preserving PPE to clean lift stations, bathrooms, trash cans, and man contact stations requires extra staff that normally would not be needed this time of year and burn rate of PPE goes up exponentially. There is a high burn rate on PPE. I do fit testing for N95 masks our LEO only, no other staff are fit tested for PPE. They get masks when available.
2A Part time staff and students aren't available like they are during peak times like summer.
3. Local and state governments are pushing stay at home, but yet lets open up parks and let people congregate at will.
4. Revenue funds are limited see #2
It sucks yes, but an ounce of prevention is worth a pound of cure.
Complementary pic of one of our lake beaches for reference: remember no bathrooms, no changing areas and no concession.