I have hosted in Iowa state parks. There is a 14 day stay limit. On major holidays the parks filled up fast 13 days before the holiday. I don't mean physically filled up but most or all sites were tagged and paid for 13 days before the end of the holiday. Once paid for they do not need to be occupied for any or all of the 14 day period. Nothing needs to be parked on the site as long as a paid for tag is in the window. That's $182 of revenue per site for the period. If the site is paid for and the tag is removed and occupied by someone other than the original camper I can guarantee that person will be escorted out of the campground and lose any fee they paid. I would bet that most sites are spoken for by now for Labor Day weekend by now.
Also half of the sites in most parks are can be reserved 90 days ahead of time. Most are reserved 89 days 23 hours and 59 minutes before a major holiday weekend. Occasionally someone will not show and not cancel. The site is still theirs as long as they paid for it, whether it is occupied or not.
We have never heard a lot of negativity about this policy.