Those people shouldn't be registering to vote several times. I would guess that most of them didn't even go to the polls to vote.

When you are living in the poorest part of town, you will have several nice people come to your door prior to an election. Some of these nice people might even give you a twenty dollar bill if you will simply register using one of their forms. The various voter registration drives are not organized into a single administration. The continuous overlap that occurs on your front porch is a nice supplement to your fixed income. "Have you registered to vote"? "No, I don't get around like I used to." "Here's twenty bucks. Just sign here". "OK, thank you very much".