In my experience, at least in US, less than 1% of medical students go into the field "to help people." In fact, nowadays saying you want to become a doctor "because you want to help people" sounds almost cliché. Most of them do it either for money, social status or because that's what their mom wants them to do. And while it's true that very few programmers are "incentivized by positive social change", many of them do it because they find it interesting and fun in some way.