Why don’t you use more of the screen?
We’ve deliberately designed the site so that the focus is on content and learning materials without distraction. The aim is to create a quiet and studious environment that encourages you to focus. The central content column and the typography is designed to be really easy and comfortable to read (making the column wider makes it harder). We also want to provide a consistent experience across mobile, tablet and desktop and so our page layout adjusts to whatever size screen you happen to be using.