Not sure. It's hard to analyze as it's more of a visceral impression. It could be in part the way natural environments tend to structure themselves over time, like how we throw our stuff around in natural ways.
But also, the design often adapts to the capabilities. Games like GTA3 used to have thick fog just to hide the fact that they couldn't render stuff far away in time. You can say that's an artistic choice to give a smoggy big city atmosphere, but clearly it was a practical choice as well. Even today, game designers like to make things dark, blurry and rainy, so that the un-realism becomes less obvious.
But also, the design often adapts to the capabilities. Games like GTA3 used to have thick fog just to hide the fact that they couldn't render stuff far away in time. You can say that's an artistic choice to give a smoggy big city atmosphere, but clearly it was a practical choice as well. Even today, game designers like to make things dark, blurry and rainy, so that the un-realism becomes less obvious.