The way it was explained to me was that the Jews loaned money to people over many centuries, a practice not common in other religions.
Muslims did not, and Catholics frowned on loaning with interest. There is a certain term they use which i forget.
Usury. The term is still used for excessively high interest rates that may be illegal, and also used by those who think, as many in the Middle Ages did, that all interest is immoral.
With exclusion from "respectable" occupations and even segregated away from the feudal system of Christian lords and serfs. It seems that over the whole Middle Ages and into the modern era, Jewish people were associated with finances and trade. The many expulsions of Jewish people from cities and kingdoms may have had financial motives but could also be motivated by accusations of crimes and sacrilege.
