Ya know, even nowadays in the 21st century, there are many places around the world that are filthy and squalid, like in Brazil and Africa, there are towns were it looks like Jabberwocky, if not worse.
But like Iliana said, the developers weren't very good at pulling the "filthy" look off, probably because they didn't care. After all, it's just a video game. If Bethesda made a video game of Compton or Inglewod, California, haha, man, I'd sure it would look nothing like what it really is. Or hell, even downtown Los Angeles with its myriad of homeless people pissing in alley ways and what not... Bethesda would probably make it look like Beverly Hills because they're too time pressed to add in trash and filth. Ah well, that's a computer gaming business for ya.