Why? Because people who don't wash their hands, are dirty.
Also, if i had made this chart, I would have added use a paper towel to open the bathroom door on the way out. That way you don't get any of the germs from the other dirty people.
This post has received quite a few hits, so we wanted to make it clear that we did not make this chart. We found it here: handwashing
since this post seems to be so popular I wanted to put up another more advanced hand washing chart.