The dealership gets zero value from giving perks to non customers. Disney gets tremendous value from repeat visitors regardless of where they purchased their points.
Disney Vacation Development makes profit selling direct to customers. DVD doesn't make any money when one DVC member sells their contract to someone else.
They want to...
A. Force more direct buy.
Obviously, that is the point of any marketing campaign - to get more people to buy your product.
B. Extract a teeny tiny bit more money out of those that choose resale.
DVD doesn't make any money off a resale. DVC had a member who owned the points before, and after the sale, still has a member who owns the points. To DVC, it's just a name change.