I think you have your dates a bit out of sync. The boatloads of Jews were turned away during the war, not after the Nazis lost and had their scientists deported to various victorious countries to aid them.
Ideas never die. Good or bad, they just get recycled. Eugenics is a very old idea. It is probably as old as the first social animal with its herding or social instinct. It is a rationalization of a primitive instinctive drive.
Mendelian genetics strengthened this mechanism by showing the mechanism of inheritance. Knowing this and not knowing about how environmental changes could be inherited, and not knowing the full extent of the influence of the environement briefly biased the world towards racism and Eugenics. This produced Nazism.
Modern science, by discovering how complex inheritance and environment influences actually are are weakening this instinctive bias.
