That is because they are private CGs and have an agreement with C2C, RPI, AOR, ROD.
All of those are just 'camping programs'......they do not have CGs.
The private CGs give priority to their members......special times, holidays etc. and allow 'affiliates' to use the cg at other times for a reduced rate.
Same way YOU would have priority at your home park over 'outsiders' during special times/holidays.
We used C2C for 7 yrs. of full time travel. It helped to greatly reduce our 'site' fees. We traveled weekly/2 weeks rarely staying in one area for any extended times. At $10/night we enjoyed staying at private CGs when available.
When a private CG had black-out periods we used other types of CGs......public, COE, city parks, fairgrounds, state/federal, boondocked (never at Wally World).
And we used Passport America (50% off daily fee) when available and sometimes would get a 10% discount just by asking for a discount.
Just like the private CGs...we couldn't always get into some of the other options either during peak times.
Memberships work when you FT and travel coast to coast/border to border and when you buy them CHEAP via resale. We recouped our initial buy in and yearly dues easily the first year and then the yearly dues were recouped within a couple of months because we bought cheap and used it. But we traveled taking advantage of the different 'affiliates' when we could.
They don't work if you stay put....stay long term...go to same area all the time. And the number of CGs participating has been reduced.
Everything has exclusions/limitations......warranties/insurance/coupons/gallon of milk. Just have to work the system/use it.