Because it's well oiled, I can't wear pants without THEM getting well oiled as well.
That's the purpose of the chain guard. For the pants. Otherwise you gotta use a rubber band, or tuck one leg into your sock. NOT COOL!!
EDIT: even if the chain pops off, with such a chain guard, you won't get any grease on your fingers, or won't need to carry a napkin.. particularly with a setup that requires lining up TWO chains!!