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.
My Kindle never saw any WiFi connected to it. Everything goes through Calibre. I only read dead authors, so I don't feel bad about pirating my books.
Sometimes I go buy used books at my local bookshops just because you should support your local bookshop.