Amazon still charges ebook publishers the same “delivery fee” for each sold digital copy (US$0.15/megabyte) as it did in the mid 2000s when Kindles came with 3g chips.
The Amazon flywheel is all about reducing costs to consumers. The moment that stops happening, consumers can get caught by offers elsewhere, and the flywheel can start to go backwards.
In two decades, since 2006, they've only come down by about 50%.