I believe the main reason is the number of campsites and the amount of folks allowed on a campsite. There are only 700 some odd campsites
If they opened this up to the campsites, don't you know that all the locals would be booking the campsites up to the max with 10 folks per site and not even stay there!! They would do it just for the free food. The campground would be totally booked, BUT EMPTY!!!
I know many locals do this at the Values already, but there are some 7500 Value rooms, so they can absorb this.