Where will these drivers materialize from? If it were economical to do so, Amazon would cut out the middle man and do it themselves.
There are plenty of people who would like to be drivers. Labor participation rate is well off its highs.
The issue that the drivers need to be supervised. The local "owner" is the one who provides the local supervision. I am viewing this as sort of like a fast food franchise. A dedicated person with his own money invested can do quite well, and Amazon would also benefit.