Just design generally, including their website ... anecdotally, so many people I know don't really know that Amazon Prime Video exists, or if it does exist how to find it. Likewise for Music.
Apple has this discoverability problem too (Apple Music doesn't have a web UI, it might as well not exist if you can't install iTunes, and then Apple wonders why its social features don't take off).
For its devices, Amazon also seems to share Google's general obliviousness, e.g. they just announced an alarm clock with a camera. Who wants a camera pointed at their bed all night? Their Fire Phone pioneered this over-expensive faux-3D UI, which on paper sounds great, but anybody could have said they weren't going to get the development support they needed to really sell it, and most users aren't going to care. Design is more than just veneer, you've got to make stuff that people want... Amazon's current approach seems to be "well if we just sell it cheap enough, we'll get customers."