Why my site doesn't and will never limit line width

A lot of websites today limit their text width or user interfaces to some fixed size, and if you have a screen that can display wider text or a wider interface, you're just out of luck. This is incredibly frustrating to me, as I hate wasted space in user interfaces. Wikipedia, Tumblr and many others are all guilty of this. If you don't like the look of text reaching all the way across your screen, you always have the option to minimise your browser window, but if I decided for you how wide is wide enough, then you'd be able to do nothing about it. I prefer to give my readers the choice!