Ok. My eyes agree with Paul. Even after viewing this enlarged picture, it appears that the sides are gone or at least lowered so as to not be visible.
This picture, you see light color horizontal lines that are similar in color to the foreground. I submit that, that is exactly what it is. I do not see any visible side and I base this on the corner post in the enlargement. You can see the far post and the shadow cast that defines the inside of the corner. This is visible, unobstructed up and down. If the horizontal lines are the inside of the wall, it would continue to the inside of the post and change the view of what is in the picture. Even the second car, despite the load, appears to not have any visible wall on that same side.
So, I submit, that for ease of loading and unloading, the sides were removed to aide in this process. And perhaps these cars were purposed for this task and transloaded to “shipping” cars.
Phil