Every business segment has distributors Building trades, food service, office supply, auto repair............ A carpenter can call his supplier, and ask for penny nails to be delivered to a jobsite. A plumber can call for a rubber washer, or a couple of couplings. Pricing is also at a different tier. That shop gets free delivery, and pays less than the full retail. In some cases, they even get pre-negotiated discounts and rebates based on volume. The shop could get a $0.25 oil drain plug gasket delivered for free, and pay less than $0.25. But at the end of the day, how much do you think that shop is ordering in 1 month? How about in a year? Once you figure out that a distributor is supplying XXX number of shops, and the revenue it generates annually, then you'll understand.
Distributors delivering free is common, customary, and ordinary. If they lost money doing it, then they would all stop delivering for free. Look around you. Amazon delivers for free. Even Costco delivers for free. Free delivery is the reason why pizza and Chinese food restaurants do so well. If you sell pizza, and you don't deliver free, you would go out of business.