I get both sides. Lets say the campground is really full and there was no cancellation fee. You don't cancel until the day before - there are a lot of people that passed on that campground and made other plans. I am with you - I plan really far in advance too. Sometimes you can't get reservations even when you plan that far ahead - Yosemite is a good example. The campground might be able to get someone to reserve the site, but if they don't, they at least get your cancellation fee. Do I like it, NO, but I understand it. On the other hand, if its a really full campground and I cancel months in advance, there is at a minimum a 99.9% chance they will get someone to reserve the site and also get my cancellation fee.
Note: I reserved a spot in New York (New Jersey actually), and they have a no refunds policy. I was going to stay 2 weeks, but I couldn't stomach loosing $600+ if something went wrong and we couldn't make it. I barely could stomach the $300+ for the one week. They also make you pay 100% up front at that place.