Question: why downscale 4k to 1080p?
Answer: When you downscale from 4K to full HD, you're essentially oversampling the image to have 4x the data for every pixel. Therefore, when you have 4K footage and downscale it to 1080p (Full HD), the image is going to look better than it would at native 1080p. ... YouTube's 4K platform is otherwise fantastic for what it is.