Yes. That's what people don't get...compression. There is no way anyone is going to stream 4K video. Our internet wires would start smoking with the overloadJudging by several threads on this forum, itunes 720p content looks better than 1080p content. I think Apple is trying to limit movie sizes to approx 4-6GB max. This is a reasonable limit of course, especially when the US has some of the lowest average internet speeds among first world countries.
However, this suggests to me that Apple is not likely to begin offering 4k itunes downloads, and therefore not likely to offer 4k appletv hardware, anytime soon. Even if they do, I'd hate to see what a 4k movie compressed down to 6GB looks like.
https://forums.macrumors.com/threads/1376130/
https://forums.macrumors.com/threads/1768685/
At best you could hope for a 4K to be compressed using h.265, which might give you a little "better" quality than 1080p while staying around the file sizes you mention.