This video by MrWhosTheBoss explains it at the end of the video.
The gist: companies got your address somehow. They ship an item from Amazon, as a gift, to you. This allows them to review *any* item on Amazon, so they can give it a great review.
The gist: companies got your address somehow. They ship an item from Amazon, as a gift, to you. This allows them to review *any* item on Amazon, so they can give it a great review.