Do you know why they are specific about not sending them mail order?
It's an attempt to preserve and control the perception of the brand in order to reduce widespread discounting.
Dealers tend to accept it because by preventing out of area sales it also helps preserve their patch.
My local bike shop tries to avoid taking on brands that are routinely thrashed by the online discounters.
Trek are also able to exert more control on the dealer such as insisting they keep a minimum stock, or take a couple of the latest model they are trying to push.
Increasingly, Trek and others are adopting a business to consumer via a shop model, as opposed to a business to business (wholesaler) model.
The bike companies reduce the shop's discount on the basis they've done most of the work on a sale via click and collect on their website.
Discounts may still be available if the dealer has the bike in stock, not least because they have more profit in a stock bike than one you order from the Trek website.
If you pay Trek directly, it's hard for the dealer to offer a discount because they are not seeing your money, only getting a commission on the sale.