What is direct mail? If that's rhe equivalent of UPS/USPS, then that's a service, not a tangible good. A tangible good would be something more like a part used in a manufacturing process, which is where the commonality to food comes into play - food tends to have many ingredients that come together into a final product - but anything following this tangible good line, from my experience, will follow these terms.

The reason kind of seems to be to give more flexibility to the supply chain. If everyone required payment upfront to get items to shelves or lots for customers to buy, then the risk goes more fully on the last link in the chain. It appears this pattern began to spread the risk to the entire chain.