Lots of the 4k broadcasts are made with only HD cameras and then "upscaled" to higher resolution. And in-between the camera and your YTTV account, it probably gets compressed, scaled, etc.

Does it look better than a 1080 broadcast? Sure. Might it be closer to what a person with a 4K tv sees when their own hardware upscales a 2k broadcast. . . Yeah, might be closer.

To your point, a buddy of mine was at in laws Christmas when the opened their Blu Ray player to great excitement. They did not own any HD displays and didn't seem to get why that mattered. The Blu Ray would look better, they were sure.