This system is only employed at the most popular locations -- your random rural land isn't going to be competitive with a top-10-in-the-world attraction.
Too many liabilities, squatters, delinquents, etc for private landowners. It's a legal headache to create a "camping ground" on your property in the US.
True, though some states have 'recreational use statutes' that limit landowner liability for allowing public access to private land. But there are still many risks and headaches involved, even with those protections.