Makes me glad I stuck with D2D where Amazon is 'one among several' instead of the 'one and only.' Though Amazon is the big boy of the lot, and the others have their quirks.One concern, common to monopolistic practices more generally, is that the supplier of the service suddenly changes the terms of service to the detriment of the customer or, at the very least, benefitting the provider with indifference as to consequences to the customer.
Amazon has in the past made such changes with such seeming indifference. This doesn't mean the effects were equally bad or even significantly bad to all authors, but that's scarcely reassuring.