Everyone saying "you don't get it, you could never download a movie to an ATV4" are missing the point either unintentionally or deliberately.
In days of yore you could download a movie to your laptop or desktop then use your ATV, go to computer, then select and watch that movie. Since the whole movie was already on your computer you didn't have to worry that your internet speed was crap. It may have taken 6 or 7 hours to download but once done you could just play it.
Apple happens to own both iTunes and Apple TV. The fact that you USE TO be able to download to a computer and watch, using your computer, iTunes and Apple TV and now you can't does mean it's Apples fault, whether the functionality was removed from iTunes, ATV or both.
Apple needs to send some senior execs and technical staff to live for a month someplace where their download speed is 5Mb or less, and upload speeds are 700 Kb. Then have them try to watch movies, or back up their phone or just their photos to the cloud.
Your conclusion does not logically follow. Indeed, Apple 'owns' iTunes and Apple TV. It does not own media being streamed or purchased, however. It very well could be out of Apple's control as to whether the licensing on 4k content made available through iTunes allows for downloading.