3840x2160 isn't almost four times the pixels of 1920x1080. It is exactly four times the pixels. So every full HD content will be upscaled without any loss. One pixel will just take up four pixels in the higher resolution.
On top of that full HD already gives a very sharp image. And when you are far away enough and/or the screen is small enough and/or your eyesight is bad enough there is no visual difference between the two.