I don't know about most people but to me seeing bits of my desktop on the sides of the window I care about feels like visual noise. I like to have all my apps maximized but maybe is that just me ?
How having bit of your desktop showing on the sides any different than whatever background image or color a particular website decides to show on each side of the text?
I prefer having a quiet single color background and being able to dictate how wide is the text I am reading than being limited by the website owner's choice. But that is also maybe just me.