Because the Allied war in Europe had nothing to do with Jews. We were pursuing three objectives: 1) Liberate France and the Low Countries, 2) Protect Britain, and 3) Preserve the USSR.
Roosevelt didn't want Jews in America as refugees and was very proactive in preventing it. Stalin shed no tears over the genocide in Ukraine and the Baltic, he probably thought it was a good idea.
The concentration camp videos in "Why We Fight" were from Buchenwald and Dachau, which were very bad places, but non-denominational prisons where the death of inmates was the result of starvation and disease.
The crimes of Germany against the Jewish people in the East, and via transport from Western Europe (especially France), were never part of Allied war aims and, to the extent that most people today believe they were is an example of false memories.
Yeah, and there’s another point to be made: If people truly were concerned about the Jews being wiped out during the Holocaust, they would have doubled down on the Doctor’s Plot as soon as it became apparent (especially after it became public knowledge during Khrushchev’s secret speech), and made even MORE enemies with the USSR, instead of acting like the USSR was Jew-friendly and calling us Americans fascists.