It is true that Jews do traditionally vote Democrat (to their own detriment--people do not always act in their own self-interest), though in recent years, statistically, there is a very small, but slow creep in the numbers toward the Republican Party.
Another example where voting history does not make logical sense: It is also true that for decades, Blacks have voted in the 90+ percentile for Democrats, but what have the Democrats done positively for the Black culture?? Very little. Actually, in reality, the Republicans have historically done more for Blacks, and there is some very slight awakening to this fact, but the demonization of the RNC and the ignorance of the truth continues.
You are making the mistake of thinking that decades long voting patterns are all logic-based, but sadly, they are often just not. These voting patterns instead tend to be more of a tradition carried on from one generation to the next, with little current up-to-date hard-nosed analysis ...