One reason Jews became the bankers and money lenders was because the Church condemned charging interest. Christians could not and would not lend money and collect interest but since it was not a "crime" but a moral sin Jews were under no such restrictions. People have always needed a source of money, bankers and money lenders provided that source and Jews were the bankers and money lenders. But, then as now, people were happy to borrow but very reluctant to pay back.