It's not necessarily a scam but you misunderstand their purpose.
They are not intended to provide sites for you to stay a week in the wilderness. The idea is a winery/brewer/golf course/etc... offers to let you spend the night (typically without utilities) in a field or back lot with the expectation you patronize the business.
I do agree completely with your #2 issue. Why they would hide the locations makes zero sense. They give some BS answer about the businesses wanting privacy but what business wants to hide from potential customers.
They indicate that your purchases are the only benefit the business receives. So my guess is hosts don't really care if you are an official member. They make the same amount if you are officially a member or not. So this is a way for the parent company to make sure you buy a membership.
We considered it but decided not to join as we couldn't determine if there were sites suitable for our needs. With 1 night, it would be mostly when we were just quickly passing thru an area and if we have to drive 10-20miles off our route, it's not worth the trouble.
