The Kindle is merely a tool that helps Amazon to do what it does: sell books. (Just like printers** are devices that require their owners to buy ink from the manufacturer.) Using the Kindle itself helps keeps the Kindle user linked to Amazon, but Amazon can live with people downloading its app and buying the ebooks it supplies, because that's Amazon's main business.
** - At the moment, I test my blood glucose level once a day, but will stop once my current batch of test strips (the non-reusable part of the system) runs out. The diabetic nurse at my 6-monthly appointment said that if I'd needed to continue daily testing (I don't), she'd have given me a different brand of blood meter. Apparently, the manufacturers almost hand them out (sell them cheaply, I'm assuming), because they make their money from selling the test strips***. It would have been cheaper to give me a different meter because the other manufacturer's test strips would cost the NHS a lot less money.
*** - She told me this because I'd asked if she needed my current meter back, both because I'd have to arrange to take it in and I thought it was a valuable item. That's when she told me about the "meter cheap; test strips expensive" manufacturers' business model. The meter had no value to the NHS, because it wanted to have access to cheaper test strips. Giving my meter to someone else would have cost, rather than saved, the NHS money.
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