What are you suggesting exactly? That the maker of this hardware should do whatever it takes so that there is some official Kindle app like on Android?
I want to access my books on random devices too, which is why I never bought a frikkn Kindle book.
I did buy a bunch of Audible books, starting way back when there was nothing else, and I knew the deal when buying, so I simply went through the grief on my end to strip them (easy these days) and don't care about the legality (or rather, am willing to fight and defend the legality).
But buying something from Amazon and then complaining to anyone but Amazon that you want something Amazon doesn't provide or even allow, I don't get that.
This wish for this thing that you want should be directed at Amazon, and if you recognize that that would be pointless, well, correct, that's why you shouldn't buy a book from Amazon in the first place.
Or you should decide you don't recognize any legal conflict and help write software to uncrappify your property.
This issue isn't specific to the Kindle, you can go and buy books on Apple or Google or Kobo or Barnes and Noble and its the same story.
Many books can only be bought this way. Publishers don't want to sell books through platforms that don't have DRM, because they are scared of piracy.
It would be great if we could have open ebook reader software that could display these books.
eReaders like the Xteink X4 are beautiful but lots of books are impossible to legally read on it. Yes, I know that I can break the DRM, but I think its sad that this is the only path for legitimate purchases.