I think we need to be careful about broad statements involving the parks. Here in St. Paul, the park lands were never closed. They closed the buildings, zoo, and 3 parks near the Mississippi due to flooding. The TV news reported it a bit more broadly, which implied everything was closed. It was the same with the WI state parks, the crawler on the TV said WI parks were closed. Checking their website showed it was only some of the state parks, due to either crowding or excessive vandalism.
Personally, before I head out to a park these days, I am checking the city / county / state website to check on their current status and making sure I know their current guidelines are. In Minnesota, there are still plenty of overlooked parks within 45 minutes of St Paul where I only pass 2 - 6 people in 3 - 4 hours of walking.