You're missing the point of the PSLF. It's intended to provide incentives for highly qualified people to choose public service rather than go into lucrative careers. These are considered "useful" careers, but they don't pay well. For instance, I currently work as an individual contributor platform developer for the US Air Force and I make more than the 4-star chief of the entire Air Force, yet presumably he has more of an impact on the country at large than I do. I believe the president is the only federal employee with a higher salary than me. The purpose of programs like this is to make sure we still have people willing to work for the government at all, given everything else they need to give up to do it.