[DerSaidin]

Because 1) WWII was more of a total war scenario for the US, where a country is dedicating as much resources as possible to win (US is not doing this for Ukraine), and 2) developing technological supremacy takes lots of time, and can't be rushed, so it must be done ahead of time (and continue in peace time to maintain supremacy).

[dh2022]

I would also add that after Vietnam war America became more reluctant to put Americans in harm’s way. Is almost impossible politically to institute military draft in America: USA did not do it when it was fighting two wars at the same time (Afghanistan and Iraq).

This helps explain at least partially why America is so keen on military tech.

[tomatotomato37]

I would also add to that the public perception that a wonder weapon (nuclear bombs) ended WWII, despite the fact it was only one of multiple more mundane factors that essentially guaranteed an Allied victory (and that's only counting the Pacific, in the European theater the "Wunderwaffe" lost the war)