http://www.engadget.com/2014/12/11/amazons-android-app-has-quietly-been-removed-from-google-play/?ncid=rss_truncated

When Amazon updated its primary Android app with an “Apps & Games” section, it was a milestone in third-party distribution: Finally, you could access Amazon’s library of applications without sidestepping Google Play. It didn’t last long — Amazon’s app store mysteriously disappeared from Google Play this week. Well sort of. The URL for the Amazon app’s product page is still active, but it’s no longer searchable from within Google Play. Why the sudden return to the status quo? It’s exactly what you’d expect: Google didn’t like facing competition from within its own app store.