What sets apart video games from other forms of visual media is that the player gets the opportunity to explore the game world. To travel through the places, revisit them at will and take in observations that were not so easily accessible in movies or pictures or even books for that matter. 

So when you are in a world, even if you have limited to no human interactions, the levels are designed in such a way so as to give subtle hints to what must have transpired in there or talks about the people the culture the political scenario or even the crisis the people face.