I have come to what I regard as satisfactory conclusions as to why most Jews vote Democrat, but it is hard to condense into an easy answer.
I'll mention a few points.
They are taught to think as a "tribe." Tribes tend to be socialistic and look after everyone who is considered part of the tribe, and so the idea of looking out for everybody appeals to people who have this mindset.
Tikkun olam. The idea that you should make the world a better place. If you think it is your duty to make the world a better place, and you are okay with using the tool of Government to enact that idea, then you will tend to support the party that likes using big government for things it wasn't designed to do.
Lots of Russian Jews in America. Their families came from Russia, and have the socialist mindset that a lot of Russians had, and from what i've been told, this socialist mindset goes way back before Lenin ever brought Communism to Russia.
Year ago I spoke with a guy who said he was a German Jew, and the German Jews were far less favorable to Socialism and much more oriented to Capitalist economics, but unfortunately Hitler killed so many of them, that they are much less influential than the Russian Jews.
They vote the way their families do, same as everyone else. If their fathers and grandfathers voted Democrat, they will tend to do that as well.
Anti-Christian sentiment. As I said in an earlier post, a lot of older Jews were coerced and disrespected because they would not adopt Christian viewpoints, Christian holidays, or convert. A lot of Christians back in the day were obnoxious @$$holes, and would not stop pressuring and maligning them regarding conversion, and a lot of people have resentment towards people who are overtly Christian, and do not want to support them because of their bad memories.
Years ago I spoke with an older Jewish woman who told me about how miserable they treated her when she was a little girl. I've seen other accounts of such treatment online and in videos.
Just a few points that if you look into them with more depth, it makes it far easier to understand why most Jews tend to vote Democrat.
Even I as a lifelong supporter of Republicans, have soured on the party, but there is no alternative, except to replace the party establishment.