Nobody said that FedEx should build their own server hardware. And that's what you are comparing it too.
FedEx could just buy server appliances from e.g. Dell (buying the Boeing jet) and operating it. Because paying some other air cargo company will eat a lot of their margin, the same with Cloud infrastructure. They are not a startup which could better invest their time in development, they can without any problems hire some people to administer their server fleet. When they switch to a cloud they will likewise hire some engineers only managing e.g. AWS to administer it.