Amazon is part of the problem. Amazon has agreements with with all the major shipping companies to handle packages that Amazon can't deliver themselves.
Now that ordering groceries and common household items has become popular, the demand for shipping has skyrocketed.
I worked for them for a year. The automatic shipping label application machine could get a minimum "bid" locked in from the shipping companies in the time it took a package to cross the scale and make it to the applicator head - about a meter away. Then they'd all go round into this gigantic ship sorter machine, which directed the packages downward toward the right shippers truck, where it was loaded manually.
Of course, as with any fully automated system, it would mess up from time to time. They solved it by getting agreement from all the shippers to "just deliver it for us anyway" if, say, UPS got a FedEx labeled package.
