We could have and should have. WWI was a waste of American blood and treasure in a war we had no business being in.
We had a real motive for being in WWII - fighting an ideology that had designs on America and which was incompatible with the American way of life and our national interests.
Because of the debacle that was WWI, Americans were extremely averse to going to war in Europe again and allowed a bad situation over there to fester until it was almost uncontrollable.