It's actually a result of the Cold War. There's a lot of overlap between environmental and anti-war groups in the US, and during the 60s and 70s sentiment against nuclear weapons started picking up steam. Then after Three Mile Island and Chernobyl, that sentiment entered the mainstream, expanding to also include nuclear energy in general. Since coal was still king back then, most energy companies didn't really care to try to change the new public disapproval of nuclear energy, so it's mostly persisted into the present day.