I can't give you anything more than educated guesses, however you're talking about a time when nuclear energy wasn't widely understood and probably had a fantastical aura around it. Slowly the cons became as widely known as the pros and that changed. Nuclear energy is actually rather safe, but it is also expensive. Plant construction and the storage and disposal of the spent fuel assemblies - all expensive. The accident in Ukraine (major) and Three Mile Island (minor) severely damaged public opinion and the NIMBY crowd pounced. No one cared the design of the Chernobyl reactor was ass backward or that operators were performing unsanctioned and probably illegal tests which caused the meltdown. The problems in Japan have not helped.

My point is, it was all very new and there was a hopeful promise of free energy, unrealistic (in hindsight) though it was. We were all just out of the worst war in history and everyone was looking to the future. People needed that.

Something else to take into consideration was the Cold War, suddenly it became a very possible reality that another country could unleash this modern horror onto the United States and the promise and wonder of an atomic world didn't look so wonderful anymore. We had schoolchildren hiding under their desks, drilling in case a bomb dropped which certainly changed the way people looked at the idea of atomic energy.