It’s not… They’re DRM and encrypted… I have - in the past - where the last 2 books in a pentalogy were only available for Kindle - purchased them - then used my work Windows 10 laptop (because I had no other Windows systems) to decrypt them - convert them to un-DRM epub format - but - what a pain! I think it was standalone exe file or something… But it worked…
My e-reader back then was a Kobo Aura - and you can’t do Kindle (or Google, or Apple) e-books on there - just stuff purchased through Rakuten/Kobo - or un-DRM epub (I managed them in Calibre). This locked in ecosystem is why I switched back to using an iPad (mini 6") to read e-books… And using a more multi-purpose device - means I can e.g. jump to Safari and look at a map - or open a bitmap image of a map of some fictional place…
I remember there was supposed to be some plugin for Calibre that would decrypt DRM ebooks - but I NEVER got it to work…
This Reddit post is about Calibre on “PC” (i.e. Windows) : https://www.reddit.com/r/Calibre/comments/1c2ryfz/2024_guide_to_dedrm_kindle_books/
Yup! I posted something elsewhere on here recently about using the “recode” utility to replace “diacritics” on vowels (with plain latin vowels) in an epub file (Recode utility - CLI)…
I sometimes also unzip epub files to extract things like maps - as I find it nearly impossible to flip back and forth between a map, and the narrative…