"Over the last three years, Prime Video has become an important part of Prime," the statement says. "It's important that the streaming media players we sell interact well with Prime Video in order to avoid customer confusion."
http://money.cnn.com/2015/10/01/technology/amazon-bans-apple...
Combined this with Google's relatively secret (but well known to you, oh avid reader of my comments here) Mobile Applications Distribution Agreement (or MADA) which places heavy requirements on what Android devices can be if they have Google Play Services, like forbidding so-called "incompatible forks".
I mean, bitmapbrother, it only makes sense that Amazon only sells products compatible with their own products. The Apple Store doesn't sell chargers for the Galaxy S8! That would be madness. If Google wants their products sold on Amazon, they should feel free to loosen up their license restrictions to permit compatibility.
Also, Amazon is free to use Google Services providing their devices pass the CTS. In fact, their rumored Ice phones will use GMS.
Can you please cite where you got this information from?