I think Jewish devotion to radical Left politics originated in Europe as a response to anti-Semitism, especially in Eastern Europe. In Russia, under the czars, and in other parts of Europe, Jews were often prohibited from owning land and were herded into ghettoes and were the target of state sponsored pogroms. Of course many were downtrodden and impoverished. This environment may have caused many to embrace Marxism, Bolshevism, and Socialism and this radical politics was brought with them when they immigrated to America.
I think that accumulated anti-semitism is part of the story, as you say. Long oppressed Jews wanted something “new.”
I think another part is that the religion itself is unsatisfying to moderate and reformed Jews, who are more culturally Jewish than religious. Liberalism is a religion, although a defective one, which supplements what they miss.
Another factor is that in the early part of the 20th century, a lot of Jews were poor, and the labor and other Democratic initiatives were helpful to them and bought their loyalty. Besides, they weren’t all that well thought of in WASP America. A lot of these attitudes transmit through for a few generations.
Excellent observation-I think your explanation goes a long way plus blue-blood old Yankee money Republicans were not exactly welcoming.