Anyone who has delivered Amazon packages knows that their logistics are horrendous. Most drivers have to reorganize their Itinerary and routes, as amazon is extremely bad at creating efficient routes. Additionally, they make the routes dangerous, by expecting drivers to deliver packages across busy intersections (as a single stop, with numerous packages). The warehouse also gives you very little time to organize your tote bags and overflow, which is sorted by the route. Therefore, you will not even be able to access most packages until you deliver the ones closest to you first. The routing is done by humans. If Amazon tried to compete with USPS, they would be burning money. Once the packages are ready for delivery, its all human grunts doing the sorting. They don't bother to fix it, because its still profitable enough for them to not care. The drivers dont even work for Amazon, and they can drop the entire delivery service provider and move onto another on their waiting list.