I have direct experience interacting with the Amazon delivery partner fleet operations. I don't disagree, I would like to add a few details to the discussion.
There's one important nuance missing in all this and that is that the Fleet contractors, those who own and operate the ProMaster and MB step-vans, they are "independent operators" who are sole suppliers, totally beholden to Amazon. I suspect it is extremely limited to what extent they can leverage any power against amazon, aside from of course striking the means of production, likely forfeiting their work.
The arrangement makes these events, to my mind, look like a much bigger sacrifice than it would in a normal market. I mean, just like you said, they up and closed shop rather than keep milking this cow! Maybe it's a bit sour.
From what I can gather, the fleets are assigned routes and duties, and are prohibited from using their capital (The blue Amazon fleet vans) for other business prospects, obviously. This makes sense because it says AMAZON on the Van, and the Drivers wear Amazon uniforms. But these are ostensibly independent small businesses.
Amazon, I believe, does front the capital expenditure for the vehicle acquisition, and they also require the maintenance to be accomplished on schedule or they levy a fine. The Operators take all the busines and insurance and training and health risks, and I'll bet there is no stipend for "PTSD from 5 more unreportable near miss accidents today." I worry that there is nobody with this kind of fleet logistics experience overseeing these operations.
When Amazon decides to re-organize routes, the truck operators may find they are operating at a now reduced revenue stream, with no alternative but to acquiesce. Their fixed expenditures don't change too much, and while they still need to maintain the fleet and make choices about that, their payroll, etc with the added uncertainty of whether or not Amazon is gonna throw them a bone, I have witness that they are cutting corners.
They can't liquidate the vehicles, because they are now drastically devalued from normal depreciation, Amazon branded (probably bonded somehow) and these things are pretty banged up. Also, I digress--the ProMasters kind of suck, but they do seem to keep cranking for now.
It may be that perhaps those operators who cannot adjust to the required efficiency in operations should go under, forfeiting their start-up capital, but Amazon deigns the start-up worthy or not, and bequeaths the start up cash to these guys and gals. Amazon can leverage their incredible reputation, stock value, and cold-hard liquid cash to get the best deal on credit in a market where the interest rate is Zero. I don't know what the operators pay--but becha it ain't zero.
I feel uncommonly conflicted about this arrangement.