Well no, it's not. You're purchasing a license to consume the content, conditional on the terms of the license. What gives you the impression you're buying the book?
If amazon really wanted the customer to understand the fine-print, they could force that. They don't, so why should customers care?
[0]: https://www.howtogeek.com/162994/how-to-strip-the-drm-from-y...
[1]: https://apprenticealf.wordpress.com/2012/09/10/drm-removal-t...
None of this by itself is promotion of piracy as far as I'm concerned, since we're just talking about gaining full control of the things we DID buy and paid for from Amazon, so I refuse to consider it "wrong" despite their tiresome efforts at DRM lock-in.
https://www.dedoimedo.com/computers/calibre-kfx-drm-guide.ht...