The reason we didn't go after the Japanese and German people as hard after WW II as we did after WW I, was two reasons:
1) The American leadership saw that embittering a former enemy will only lay the groundwork for another war within a generation.
2) We needed allies and bases to stand up to the Russkies during the Cold War.
We let many, many Axis war criminals off the hook for the reasons you listed. There was quite a lot of: The war criminal is sentenced to death, or life imprisonment...soon after the sentence is reduced...soon after the war criminal is released because of "poor health".
I certainly understand the reasoning there. But it made a mockery of the victims of the Axis.
And the Germans were pretty good at building missiles, jet engines, and that stuff.
The third reason being that Japan was allied to us during World War I.