I imagine Amazon wouldn't be opposed to preinstalling the Play Store. But getting permission from Google to do that comes with a long list of requirements. You

I imagine Amazon wouldn't be opposed to preinstalling the Play Store. But getting permission from Google to do that comes with a long list of requirements. You are either at the mercy of Google's requirements and conditions or you develop replacements for every Google App (which are way more than most users realize). Amazon are basically the only company daring to try the latter path.