The vast majority of readers are loyal to a single digital bookstore and do not comparably shop around to find the best deals.
Amazon, Barnes and Noble and Kobo all try and lock you into their ecosystems. Their e-book formats do not play nice with each other and it’s almost impossible to transfer your purchases from one company to another. Barnes and Noble actually disabled the ability to backup your e-books last year, because they did not want people making local copies or striping the DRM.
All of these companies do not really need to do anything to retain their customers. The readers who do business with them are not very likely to jump ship and start buying e-books form the competition. One of the drawbacks of this mentality is that it is creating on air of stagnation for companies such as iBooks and Google Books, where there is never any innovation. Their e-reading apps haven’t changed at all since they debuted five years ago, nor are they appealing on prices alone.
The loyalty that people display towards a specific bookstore results in an uphill battle for new companies to be financially viable. This is likely the chief reason why Txtr, Blinkbox Books, Oyster, Entitle and FlipKart all shut down or went completely out of business.