Because the crimes of the modern Israeli state are not an inherent aspect of being Jewish, and many Jews are skeptical of a party unconditionally defending it.
But Palestinian American voters trend Democratic, why would Jewish voters want to stay in a party that is heading towards a more pro-Palestinian bent?
There is a reason why the Jewish vote is for the taking for Republican candidates in the Northeast and so on.....
Jewish voters should be more Independent-minded, should be voting more Independent....
How about you don't tell Jews how they should and shouldn't vote?