In isolation, "last read page" could surely be E2E encrypted. Amazon would know that I'm using a Kindle app or device, but everything else could be opaque.
There's no motive on Amazon's part to do it this way, it would be a hassle to implement, possibly not great for battery life, and I expect that users don't care much.
Frankly, I don't care much, in practice. In principle, yes; everything which can be kept private, should be. But Amazon knowing what page I'm on just doesn't discomfit me, the way the prospect of some company being able to read my messages does.
The pro-privacy crowd needs to choose it's battles.
The most common response about online privacy is "what does is matter if X knows Y? I've got nothing to hide".
People already don't care, and I guarantee they also don't care that Amazon knows what page they are on in the book the are reading. There are much bigger issues to focus on
There's no motive on Amazon's part to do it this way, it would be a hassle to implement, possibly not great for battery life, and I expect that users don't care much.
Frankly, I don't care much, in practice. In principle, yes; everything which can be kept private, should be. But Amazon knowing what page I'm on just doesn't discomfit me, the way the prospect of some company being able to read my messages does.