The campgrounds offer it because it tends to rents sites that would otherwise remain empty. Consequently the campgrounds have limitations to its use. Some of the most common are "it can only be used certain days of the week"; "it can only be used certain months of the year"; or "it can only be used one or two days at a time." Some will say only the inferior campgrounds offer it. We have not found that to be true though many of them are, there are others which are very nice, not resorts but nice.
If you can live with the limitations and used it three or four days a year, it is well worth the money.