I agree. When Amazon sends an order using one of these type of delivery services, they should send a followup email to the customer in a day or two after delivery asking for a simple rating on the delivery experience.
Amazon is a rather wealthy company, are they really cutting corners on this key part of the customer experience because of money? Because good drivers would line up if they paid properly... or just hired a real delivery company.
Unless their copy on the website is a lie, the rates they're offering for courier jobs is actually quite competitive in the Seattle area. It's probably more about being able to control their own delivery experience than it is about cutting corners.