If I had to guess I’d say it’s a combination of 1) The Jews of European descent don’t really identify with Israel 2) Even Jews that do identify with Israel see the Democrats as being pro-Israel enough and 3) Jews tend to be more socially liberal, even though conservative economic policies favor the wealthy, and thus benefit many Jews.
And the reason Jews tend to be socially liberal is the historic emphasis social conservatives have put on Christian values, causing Jews to feel excluded or to wonder where they would fit into the conservative vision of America. I do believe conservatives are improving in this regard, with references to our country’s Judeo-Christian heritage instead of stating our heritage as exclusively Christian, and we are being rewarded with a small increase in percentage of Jewish votes won. It’s still not enough to prevent another Democratic victory. Even if all Jews voted Republican they’re too small a percentage of the population to swing the polls. The main advantage to winning the Jewish vote would be an increase in funding for our side.
Just my 0.02.
Another reason was in the early part the 20th century the elite universities, law firms, banks, brokerage houses, and social clubs were all run by the country-club Republicans (the RINOs of their time). When the Jews came knocking to join, the Republicans slammed the door in their face and they have not forgotten. The urban Democrat machines were more than willing to admit them. The Republicans have paid ever since.