Although there are hundreds of other e-book sites, Amazon has both the largest selection of books and over 70% of the market-share for digital books. In addition, their Kindle application provides a very robust user interface. The e-book model eliminates the need of any inventory and enables authors to maximize their net profit for each book sold.
The advantage of the KDP program is the removal of any and all middlemen. For decades, different types of self publishing companies provided authors entry to book sales only to reap a lions share of the profits. The KDP program empowers authors to publish their books on the largest platform and collect 100% of the net profits.
Amazon's management portal provides authors will real-time sales data for complete transparency.