There have also been cases where a customer violated Amazon's terms of service and lost access to all of their Kindle e-books. Amazon has all the power in this relationship. They can and do change the rules on us lowly peasants from time to time.
Note, there are indeed ways to download your books and import them into something like Calibre (and remove the DRM from the books). If you do some web searches (and/or search YouTube) you can probably figure it out.
Kindles have always slotted in as somewhere between the mass market paperbacks and trade paperbacks. Cheap books you read once or twice and then likely never again. If you do get in the mood to read it again? mobi files hold up a lot better than pulp designed to decay in order months but MMPBs always had a tendency to be lost forever just like amazon has a tendency to fuck with your library.
A knowledgeable user will be aware of these shortcomings of so-called "ownership" of digital goods, but the average person doesn't read license agreements and does not understand that their purchase can be revoked at any time by the seller.
The average person makes a purchase and expects to own the item in question.