Why does it use less than half of my monitor width? I'm on a 1920 x 1080, and the feed pane is only 770 pixels wide - and not resizable. What's the purpose of t

Why does it use less than half of my monitor width? I'm on a 1920 x 1080, and the feed pane is only 770 pixels wide - and not resizable. What's the purpose of this? Most of the screen estate is wasted for a wallpaper of author's choice, instead of displaying the content I'm actually interested in. I find this design choice really hard to understand.