Pure ignorance.
After slavery we were hunted, literally. We were blocked from education, from owning land, from working jobs or owning business. If we made too much money cops were sent in the day to harass or at night in their hoods to scare us or kill us. I don't know the specifics of what Jewish people faced after the holocaust, but it damn sure wasn't that. Fairly certain places like America took them in, albeit with a little prejudice. Nothing compared to what blacks had faced for centuries up to that point.
And by the way, if a Jewish person thinks its in their best interest to not appear Jewish because of prejudice... they can make changes accordingly. There is no hiding that you're black in a racist system against you.