White space isn't wasted space. It makes the page infinitely more readable to limit line lengths. Yes, you could have reduced your window width before. No, you shouldn't have to do that to get a comfortable reading experience.
Making more than half the screen white space is wasted space. The point of resizable windows is to be able to adjust the content as desired, so it's pretty ridiculous to argue that everyone else should suffer wasted space because long lines are scary.