How about because they tend to be social activists and believe in change in this life, not in some afterlife. There tends to be more focus on this lifetime, not some after life.
True enough but it doesn't explain why socialism rather than free market ideas didn't grab hold
It did in the first wave of Jewish immigration. The German Jews in Cincinnati today retain a free market outlook and vote majority Republican. The second wave, from middle Europe and Russia were majority left the day they set foot in America.