Fellow Jew here, if the name wasn't any indication, and the trope seems to have its base in, unsurprisingly, money. The short answer is that as Jewish people lent money and charged interest to their Christian and Muslim neighbors, they accumulated wealth and were able to utilize those financial resources to acquire power and influence in the Western world.

As far back as the Old Testament, Jewish people have complicated laws and regulations on usury, or the allegedly immoral lending of money with interest. For instance, Exodus teaches the Israelites that "if you lend money to any of My people with you who is poor, you shall not be like a moneylender to him, and you shall not exact interest from him" (Ex. 22:25 ESV). For the Jews, loans were meant to be a form of charity, and while it was acceptable to expect repayment from the loanee, the loaner could not ask for interest on top of it. Historian Paul Johnson points out that "among the Mesopotamians, Hittites, Phoenicians and Egyptians, interest was legal and often fixed by the state. But the Hebrew took a different view of the matter" (A History of the Jews). Even in the time of the Second Temple, the forbidden practice was so commonplace that the Jewish rabbi Jesus of Nazareth attacked the interest-charging moneychangers in the Temple, if the Gospels are to be believed (John 2).

However, none of this is to say that the Jewish people held exclusive claim to the forbidding of charging interest, or that loans for a business were unheard of. The famous Code of Hammurabi laid out guidelines for mutually beneficial loans that could be repaid with interest for the sake of a business, but still opposed loans that needed to be taken out for the sake of survival. As in, if you were a farmer and I was a fisherman, I could borrow money from you to build a new boat on the condition that I would pay you back with interest; however, if it was a slow season for fishing, it would be frowned upon - though not expressly forbidden - for you to give me a month's worth of food and expect two month's worth back at a later date.

Outside of the Jewish population, the charging of interest on a loan was considered immoral by a great many in the Roman Empire, some 1500 years after the Code of Hammurabi was written. The historian Cicero asserted through his mouthpiece Cato the Elder that usury was akin to murder, since the extraction of interest from someone in dire enough straits to require a loan was cruel and unjust (Cicero, Hannis Taylor). So, in an ironic twist, the Hebrew people seem to have influenced their neighbors out of the practice of charging interest to the point that it was commonly accepted as immoral - an immorality that would soon be turned back against them.

As the world grew smaller under the expanse of the Roman Empire and the Pax Romana, Jewish people were brought into more and more business dealings and social interactions with their pagan neighbors, and, as a result, found themselves slowly pushed to the fringes of society. Much of this stemmed from the Biblical accounts of the death of Jesus Christ, which slowly shifted the blame of Jesus' death away from the Romans and onto the Jews, as early Christian authors became aware that Rome could cause more problems from them than the Jews could. For instance, contrast Mark's account of the Passion with John's, written some 30-50 years later. Roman authorities transform from actively malicious against Jesus to objectors who reluctantly send Jesus to die for the sake of keeping the peace with the rebellious Jews. All of this would be compounded as Christianity became the religion of Constantine the Great in the early 4th century and eventually the state religion of Rome after Emperor Theodosius' Edict of Thessolonica in 380 AD.

None of this was helped by the stark difference between Jewish and Christian theology. For the Jews, faith was a profoundly personal matter and ethnicity, coupled with the bonds of a strong family and community, mattered far more. Even Gentiles who obeyed the Seven Laws of Noah could be considered righteous before God. Evangelism and community outreach were less important than one's personal faith; even, as many rabbis argued, unnecessary and impossible, since God's will pre-ordained all, and salvation was meant only for those born into the Tribes of Israel.

Christianity, on the other hand, preached a message of evangelism, spreading the Gospel of Jesus, and reaching as many people as possible. From Jesus' final recorded words in the Gospel of Matthew commanding His disciples to spread the message (Matt. 28), to the conversion of Jews like Saul of Tarsus (Acts 9) and ethnic outside like the Ethiopian eunuch (Acts 8), to St. Paul's exhortation that "there is neither Jew nor Greek, there is neither slave nor free, there is no male and female, for you are all one in Christ Jesus" (Gal. 3:28). The message of Christianity was that the gates were open and everyone could come in, as long as they ascribed to the principle tenets of the faith.

All of this is a very long-winded way of saying that, quite simply, Jewish people found themselves on the fringes of a society that considered the charging of interest immoral. Good so far?

As the centuries went on and the Jewish people became more isolated and more oppressed by their Christian neighbors, the Jewish scholars and lawmakers began to interpret the Torah in ways that would help them protect their own community, but profit off their generally antagonistic neighbors. Without getting too lost in the weeds of what specific regulations were handed down by the rabbis, or what constituted interest (does strictly money count? or can we also consider physical goods? what about the difference between a table that cannot reproduce and a chicken that can lay more eggs?), or the differences between a monthly loan and a mortgage, we can confidently state that by the 12th century, it was broadly agreed that while a Jew could not charge interest on another Jew, it was permissible to charge interest on a non-Jew, since it was not the responsibility of Jews to protect non-Jewish communities - the heart of forbidding usury in the first place. This contrasted neatly with the Christian world, which had moved from forbidding the charging of interest by the clergy (Moehlman, Church History) at the Council of Nicea in 325 AD, to denying sacraments to those who charged usury at the Third Council of the Lateran in 1179 (ibid.), to outright decrying it as a heresy by the Council of Vienne in 1311 (ibid).

So, the Jews and Christians found themselves in an interesting position. Christians could not seek out loans from their fellow Christians and Jews could not lend money to their fellow Jews, so the answer was simple. This was also helped by the unfortunate fact that Jews were frequently ostracized from most working environments and social circles, so an arrangement in which the Jews could lend money and profit without entering the Christian world, and the Christians could borrow capital for their businesses without entering the Jewish world, suited everyone perfectly fine.

However, all of this only created more problems. While tentative business arrangements could maintain the peace to a certain degree, four problems only grew. First, the increasingly ostracized Jews retreated into their own communities - not an unreasonable reaction, considering the latent antisemitism in the medieval world - but this reinforced the image of Jews as anti-social, secretive, and different from the Christians. We can't win for losing, after all. Integration to a hostile Christian society and withdraw from it both fostered antisemitism, go figure.