Mind you not this weekend but last fall a few times I drove the Motorhome up to a spot on a Thursday night (a four hour evening return drive on a work day) and book for 4 days. The campground owner is always fine with that, as I book in advance by phone and he keeps an eye on my rig. Saved us the set up time and the wife has a bad back, this way I can drive her up in the comfy truck instead of the motorhome. We rented a campground in BC years ago a year at a time. Look at Windermere and the Shuswap where you can also book blocks of time. It is after all supply and demand and we have a lot more people in Alberta now. You can buy a service and use it when you want. I can after all book a spot and not go. It's still mine because I paid for the service, the service is available to me if I use it or not. In the same campground and one that I have used in BC there are people who book the entire summer block. If you can afford it why not. I agree it is abused in certain instances - but that is economics. If I owned a campground I would love it if people booked large blocks of time, and would certainly be upset if someone passed a law that sid yo could only book in my campground if you where physically staying there.
I can't count the times when I drove to a campsite only to find it full but your make contingency plans after all.