Maybe I should have headed that "why weren't the risks obvious at the beginning?". According to the lawsuit DuPont had discovered the risks of perfluorooctanoic acid exposure by 1961. Industrial production of perfluorooctanoic acid began in 1947. Had it been a simple acutely hazardous chemical that killed rats hours after you fed them a few milligrams, the risks wouldn't have taken a decade+ to surface. I'm not trying to excuse DuPont's duplicity after they did discover problems, rather explaining why these sorts of chronic hazards are not necessarily known the first time somebody writes up a Material Safety Data Sheet.