That's a really interesting question! I can only tell you how it affected me. I checked the Striped Wall pic just to be sure.
The bleakness came for me because we are looking at a flat plain. Flat as far as the eye can see, not a tree, not a house, not a mountain, not a barn. To me an empty plane is like solitary confinement that stretches for miles and miles with only the wind for walls. The only visible sign of life is the wind blowing through the tall grass. The wind was used throughout the movie as a symbol for Jack, and the wind through the grass just reminded me that Jack is gone.
In the country, the grass is always greener on the other side of the road and we can see that what beauty the plain has is on the opposite side of the road from where Ennis is. The road stands there, cold and desolate, like a wall. Symbolically, unless life sends Ennis another miracle like Jack, I don't think he'll ever cross that road. A visual representation of so near, yet so far away.
It worked as a physical metaphor for me, because it seemed to be saying to Ennis, the one thing that made your life bearable, you had, but you didn't appreciate it and now it's gone, forever beyond your reach.