Any intermediary is only going to add more to the price, not less. If an intermediary made prices cheaper for their customers than upstream, then they wouldn't be in business.

The incentive is clearly competition from other manufacturers. In a world of dealerships, competition is murky because you can't really know the final price of a car unless you play the haggle game with every dealership. But if every manufacturer had all the final prices online, you can easily evaluate what is the better deal.