"Hotels don't do this and they take cancellations right up until the date you are supposed to check in."
Not entirely accurate, hotel reservations often have different terms, depending on the rate at which you book, and might have cancellation fees. They can even be entirely non-refundable. It can be the same for transportation, even purchases as big as cruises. Did you ever lose a $18,000 worth of cruise bookings because you chose at the last minute to cancel, or failed to get to the port in time to sail?
Many campgrounds are using third-party reservation systems, so that there is a fee to them for a booking, and a fee for a cancellation. This is case now even for reservations at public facilities. If you show up and pay the camping fees, those costs get hidden in the fees; if you don't show up, it is either a loss to the campground, or they get it from you.