The optimal width of a column of text is not a function of the container it is in, or the screen it is displayed on, but rather a constant based on the capaciti

The optimal width of a column of text is not a function of the container it is in, or the screen it is displayed on, but rather a constant based on the capacities of human vision. It's roughly empirically accepted that it's easier for us to read a block of text that flows from one line to the next after approximately 65-85 characters. Thus that extra space on the margins isn't wasted, it's serving an important purpose.