Probably has to do with the numbers of Jews in the US whose families were directly affected by the Holocaust. I don't know if there are that many Chinese families who had relatives killed in Nanking. In the case of the Jews here in the US, they have the memory of their loved ones being directly sought out and murdered just for the fact of their having been Jewish. Not all Catholics, Methodist, Calvinists, etc. were targeted in the countries overrun by Germany, just those who were guilty of opposing the Nazis, or sheltering Jews.
The Nazis also targeted Slavs, whom they regarded as Untermensch. The plan was to colonize the East with Germans and reduce the Slavs to slavery.