More specifically, the problem that frosting is supposed to fix is that light coming from a small origin is aesthetically unpleasant. It casts very distinct and sharp shadows, and to get a given amount of illumination from a smaller source requires the brightness at the surface of that source to be higher and therefore more painful to look at.
Oddly enough, sunlight is about as extreme a “small source” light as most people are going to experience. Seems to me that imitating the light source we evolved under would produce an aesthetically pleasing illumination.