Kindle was designed to sell ebooks, as people move from buying the hard copy books to downloading the ebooks. Amazon is not making money on devices, or at least not making huge money on devices. And similarly, it moved into online streaming of the video content and suddenly became a competition on Netflix. So the Amazon is very good in moving with the customer.
Since its founding in 1994, Amazon has expanded into streaming, cloud computing, content creation, and even groceries. But if traditional business strategy tells us that the key to success is focus, why does Amazon work?