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.
Maybe the technical requirements at the time were a good excuse but as soon as you demonstrate the market will tolerate that why on earth would you remove it?
To turn around the famous quote: "Amazon's margin is someone else's opportunity". :)
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.
That's not exactly true, they expanded the free tier from 1 to 100GB/mo (1TB/mo out of CloudFront) and dropped egress from ~20c/GB to ~9c/GB. This was due to pressure from the Bandwidth Alliance formed by all the other Clouds and spearheaded by Cloudflare.