Google, Apple and Amazon are all selling their own streaming devices, but want to offer their own services on each other's devices. The fruity cargo cult Apple forbids this because it means that others will have to program their devices and it does not want to show Apple fanboys that others do a better job. However it moves a lot of hardware through Amazon.
However Apple has been softening lately now that Amazon's video app finally coming to Apple TV. The relationship with Google is still rough - the companies continue to tussle over various issues, including the availability of YouTube on Amazon devices. Amazon's move to carry Chromecast could be an effort to get things on a better footing.
The products do not yet appear to be available from Amazon's site, but that could be any day now.