Because it's configurable. What if you want the lines to appear?

Then you use normal graph paper!

This reminds me of the Steve Jobs quote about sharing music without all of the Zune's software shinanigans to share a song for three plays

> It takes forever. By the time you’ve gone through all that, the girl’s got up and left! You’re much better off to take one of your earbuds out and put it in her ear. Then you’re connected