It's such a complex situation. Amazon has contracts with small companies who provide trucks and humans. Amazon provides the work, the groups of packages, the routes, the app the drivers need to use to deliver. The companies compete with each other for more 'routes' each day. They offer to take on more work, to do more. And then they hire anyone they can to fulfill those routes. The drivers themselves are on contracts…
'Who is to blame? Amazon? The companies? The drivers? Capitalism gone mad? Take your pick.' You can add 'customers' to this list since this is where it all begins. It isn't so long ago that all people complained about was the time it took for stuff to be delivered and all those 'we called but there was no one in' cards. So capitalism responded and now folks have something else to complain about.
Tomorrow if customers demand 10% of the existing prices are companies going to line up with slave labour conditions to deliver and then shift blame? Responsibility does not work like this.