I can only guess that your travels extended back before the economy went into the toilet for a few years. The RV industry, as well as the RV parks and associated industries were not spared from the down turn.
Those places that were able to survive, are still in operation, but many of them couldn't afford to stay in business, so either sold out to another company, or closed down completely. The KOA fanchise does cost money, but it really depends on the location (remember that adage: Location, location, location!) is probably more important. Plus, just how well the operators did their jobs, to create a campground that folks will want to be visiting over and over again.
We are constantly reading about some CG that the folks were just plain nasty...or the bathrooms were a mess, trash wasn't picked up, and other such things that would cause most of us to go somewhere else. And these people wonder why they are out of business???
This is a service industry.....if the service is sub-par, you're out of business. If you are located in the middle of nowhere, and only see a couple of people a year, and have nothing to offer, you'll be out of business.
It's the nature of the business.