Because even though Israel is a racist apartheid ethnostate engaged in ethnic cleansing and running fenced-in ghettos and murdering innocent people indiscriminately, it is offensive to some Israelis to compare their country to Nazi Germany.
I think there are a lot of very important differences between the Israeli government and the Nazis, although I doubt there is an American ally (or even a first world country in general) that resembles 1930s Germany more than Israel. I wonder if that's bannable.