What you're describing is the same as in any market—wholesale costs less per unit than retail because there are enormous gains in efficiency for the seller when they don't have to deal with smaller units.

In the case of shipping, I'm not an expert but I do know a few of them:

* The amount of time per mile a human needs to spend handling that shipping container is lower, because there are only a few very long legs rather than many transfers.

* The amount of time per pound of goods a human has to spend handling the shipping container is much lower, because the container is moved all at once, where your cubic-foot package has to be handled individually.

* The fuel cost per pound of goods per mile is lower with the shipping container because it is usually transported by boat and train, which are far more efficient than the trucks used in last-mile delivery.