The thing is, dealerships have incentive to keep dealerships in general in business, and they likely all know each other, so they probably won't undercut each other by a large margin. Since they all know the actual cost of the thing you're wanting to buy, dealership A gives you a price maybe a few hundred below dealership B even though it's a few thousand above what their actual cost is.

Consider how much prime real estate dealerships sit on, how many employees they have, and how many units they sell per day which must pay for the aforementioned items with their mark-up, and still turn a profit at the end of the day. Now consider how much less expensive every car would be if they didn't have those additional costs, and consider if the benefits a dealer adds are worth those costs. IMO factory-direct sales can't come soon enough.