I'm not sure if you posted the right picture. There seems to be a large amount of excess padding on the left, most likely due to a problem with the CSS style causing it to display vertically instead of horizontally (highlighted in red).
It's surprisingly obvious that this left padding when added to the current column we have on the right exceeds the width of the valuable content in the middle.
I've gone and hidden this left-padding to illustrate how StackExchange could look if this pressure were to be alleviated. Notice how the content in the middle becomes more prominent:
I apologize for resizing the images I've linked. I wanted to ensure that they would fit within the small space in the middle without too much distortion.