Vertical marketing systems have been around for quite a while. In their simplest form, they are a collective marketing activity participated in by the entire supply chain.
Just as there are a number of stages involved in the life of a product, as it starts with raw material and ends at final product in the hand of customers, so to there are stages in the marketing lifecycle of a product. At all these stages, a number of stake holders are involved and they all play a part in the process. With each stakeholder come different interests in selling a final product.
If manufacturers only expressed interest in selling their product to wholesalers, who would blame them? Wholesalers are their end customers after all. And if the wholesalers only invested time and capital into selling to retailers... same rules, right?