There are, in my experience, a lot of people sitting at home on election day thinking "It's raining. I don't want to go out." or "There's a Real World marathon on, and I'll miss it if I go vote." or "Enh. My vote doesn't really count anyway." or some such thing, and getting a call from somebody who says "I would really like it if you went out and voted." is a strong motivator for some people.