I think the real issue is that the change points out that you don't actually own anything. You just have a license to access your books via "Terms and Conditions" that may change at any time. I noticed after the first of the year that the text under the "Buy" button now explicitly states that you're buying a license; before it allowed you to believe that you were actually buying the book.
You mentioned that they killed off the "very very very old kindles". What's next - killing off the very, very old, then the very old, then simply the old kindles? Or maybe discontinuing the iOS, Android and PC versions of the Kindle app and forcing everybody to read their books on a Kindle?
None of those changes would bother me overly much because I'm locked into the Amazon/Kindle ecosystem. Sure, I'd complain about them forcing me to buy a new Kindle (same as I complain about Microsoft forcing me to buy new PCs from time to time) but I'd still buy the new Kindle. However, I would never replace the thousands of physical books that I have with e-book versions. Sure, it would save space and might be convenient but I actually own the physical books.
The issue is that people are realizing that they don't own the digital media that they bought.