Your last sentence sounds a bit condescending dude. Look, I love Red Dead, and overall I love how detailed Rockstar makes their worlds. It's just a small complaint I have.

And although the game focuses on those themes, I doubt the map design has anything to do with it. Dirt-made trails aren't really signs of modern civilization, and neither are abandoned cabins or rotted fences. They're just areas of the map for you to explore. Saint Denis alone already has a handle on the civilization theme for the game and plays heavily in the story. When Arthur and Dutch first visit the city, he says "into all that civilization?" Narratively the game doesn't treat the western regions of the map as being all that civilized. Strawberry and Valentine and Rhodes are all supposed to be pretty countryfied.