Why does America ignore it?
Well, to be fair, as with WW II, America didn’t enter until a couple years after it started. But it’s true that the Left would like to whitewash its own history of our first fascist president (and the current one, who aspires to many of the same things).
Reminding the public of WWI might also show how the beloved darling of the left, Woody himself, lied to get reelected. He promised to keep us out of the war.