Because polish are not jews. You can trash talk and joke about polish and russians even thought they had suffered a lot more deceases than jews in WW2 and not to mention during the cold war.
The fact is that there is a Zionism domination nowadays, in media, politics (Trump is pro-zionist), and pretty much else.
As the other guy said in his post, "they were polish who were anti semetist", yes, there were also bad jew people before WW2 just like nowadays. Obviously Holocaust was the worst thing in earth in WW2, and there is no justification of what nazis made, and neither you cant generalize people by their, race, religion or country. But you cant deny the fact that is hypocritical to ban people for making jews jokes but you can make jokes about everything else (muslims, christians, asians, afroamericans, indians, poles, irish, etc...).