Due to Christianity's abhorrence of moneylending on interest, the original group of levantine exiles were forced into these occupations. Now Europeans hated them for not being christian, but they were a necessary evil, rulers would essentially hold the Jews hostage in their courts to milk the tax revenue off their lending activities. The ruler would protect the Jews the best they can, but eventually the Europeans got fed up with the high interest loans and instituted pogroms. The income of each individual Jew resulted in a massive survival gradient, where the better they were at generating income off lending (and other white collar work), the greater chance they had at survival, i.e. poor Jews would succumb to the pogroms. At some point expulsions happened, Jews who had higher incomes could better survive the expulsions, yada yada yada, and that probably accounts for maybe about 5 out of their 115 IQ points. They were also forced into crowded smelly ghettos for a thousand years and were a perpetual minority, so the vast majority of crime wasn't an option or they'd get expelled, executed, ect. quite easily.
I hypothesize that Europeans have actually become more intelligent over the past 2k years or so, it's just that due to their position Jews were always 1 step ahead of them.