Considering Amazon is the largest ebook seller in the world, the paid commission to Google would be staggering. This has happened because Google has now mandated that all apps use their own billing system and will take a 30% cut out of each transaction. When trying to buy digital books, a new screen is displayed, letting customers know that in order to remain compliment with Google policy changes, buying ebooks is no longer supported.
Amazon has disabled the ability to buy ebooks in the Kindle app for Android.