I would suggest that it has something to do with the Jewish diaspora having a lot more clout and a louder voice in the USA and western world in general than those who lived under Japanese occupation.
As someone else pointed out, the horrific nature of the holocaust may be more relatable to the average American due to a similarity in appearance than say the Japanese's crimes against humanity being committed against those from Asian backgrounds who are likely considered to be more distant to many people.
Guess it's similar to the global/Western response to the war in Ukraine compared to the endless tragedies seen in Iraq, Syria, Congo, Tibet and Xinjiang, Palestine, Myanmar etc etc