There are all sorts of random possibilities that could reduce someone's life expectancy by a tiny amount but which statistically over large numbers of people would result in more than one extra death. Imagine that someone has to work one extra hour per month and there's a tiny chance of dying associated with it, or that they delay a visit to the doctor by one week, etc. Or all the other mechanisms which cause poorer people to have lower life expectancies (I highly doubt you can't think of any), which mean that someone who gets marginally poorer by a tiny amount would on the average not live as long.