The US was only in that period from Dec 1941 to Aug 1945, just over 3 1/2 years. Assuming that the build-up years (when "everyone knew" we were going to have a war) were not as intense.
I don't think most people working at home during WWII were primarily motivated by concern about their allies abroad. Instead, I'd argue the motivations were:
* supporting a friend or family member serving in the military
* capturing a new economic opportunity (government contracts, etc), following the shockingly hard times of the Great Depression
To that point, there are currently millions of people suffering at this moment around the globe. If you were motivated by compassion, you'd probably find a different job and put in long hours.
Regardless, my point is that when there is a motivating force, people work hard.