We've noticed something both odd and sad about campgrounds these days. We often find that people have made reservations for a campsite, and then don't show up. Which means that the campground is "full" but there are still sites that sit empty all night long.
In most cases, the campgrounds can't open up these sites unless they are notified that the campers aren't going to be arriving--because, as one campground host told us: "You put someone else in that site, and then at 11:30 at night the guy with the reservation shows up, and wants to know what the hell is going on."
And yet in most cases the sites do sit empty. And in many campgrounds, the reservations may be for three or four days---and the site sits empty for all of those days. Apparently, recreation.gov, or the other reservation systems, don't have a way to open these back up again. What a waste. And how sad for people who are looking for a site.
So a word of advice, If you've made a reservation and aren't going to use it, cancel it immediately and let them know. That way, some nice family just might find a campsite for the night. And with any luck at all, somebody else will pay it forward for you some day.