When you’re a company that ships billions of packages, it pays to have your own air and ground fleet.
Actually not, a Carrier is the most efficient shipper.
A Retail store, is a more expensive Carrier, because now they need back hauls to ship efficiently.
Retailers like Walmart or now Amazon, ONLY ship their EASY routes. The difficult routes they still leave for Carrier companies.
Watch for Amazon to be losing money as their Carrier fleet of trucks grow. Their transportation problems are just beginning to grow costly.