The screenshot below says it all. Could there be anything worse than making reservations and getting a rain out?

The only reservations I make are for Memorial Day weekend and maybe Labor Day weekend. Other than that I travel on off peak days and avoid weekends. I do Sunday or Monday arrivals and depart on Thursday or Friday. Some campgrounds in popular vacation areas do not allow arrivals or departures on weekend days. They want to be booked on weekends.
I can deal with a day or maybe two days of rain but not 3 out of 5. It all depends on where you are because everyone will probably have the same ideas for rainy day activities. Movies, museums, out for restaurants, etc.
I can always get a campsite up to and including the day before I want to arrive. So I watch the weather and if it’s looking good I book. Most people can’t do this and they need reservations well in advance.