One could call it a feeling of responsibility maybe. The ongoing conflicts were defining the world and scientists (and he individually) could change the course of history. I think vNM's work is equally impressive (or even more; it's difficult to compare), maybe his main contribution is starting Game Theory[1]; but because it is spread across so many fields it doesn't look as groundbreaking.

[1]: Indeed he was so confident in his work he believed he was "Starting and ending" game theory, that there would be little else to work on after his monumental work that is OTGEB. He was very wrong of course, but like other theories of the kind (Information Theory comes to mind), this early lead is very significant to the creation of a coherent field.