I stayed in a campground once this year! My TC doesn't refuse them, I just don't look for them or ever go to an area that has them.
But, maybe I could provide a different aspect. Rather than putting the spyglass on the Large Corporation, maybe the different campgrounds are not putting the code in to give you the credit? Someone pays for these benefits and credits. Years ago when I was traveling a bunch, I would stay at Comfort Inns, as they gave you a night free, after staying with them during non black out periods. Comfort Inn locations were famous for not inputing the code to allow the credit to be assigned to your account. Especially after you made the reservation with your Customer ID #.
Someone pays for it, sometimes it is not who might expect.
b