This is naive as it fails to consider that Amazon has probably made a considerable loss on the Kindle hardware business to create this market the OP is lucky enough to participate in. This investment alongside the investment in their own AWS infrastructure is why there is a reasonably sized market for ebooks right now. Also how about the cost of cellular data?
The cost might be a little high but if you don't like it, you have the choice to take your business elsewhere.
I think the complaint focused on other costs that were pushed onto the author. If amazon presented a larger cost structure (increase their per-unit charge) but covered costs like content delivery, I don't think the author would have as much of a problem.
The cost might be a little high but if you don't like it, you have the choice to take your business elsewhere.