Most of the time, it was because Jewish moneylenders were the only real game in town because the Church forbade usury (charging interest at all). The feudal system had Jews being subjects of the King instead of a local lord, they were acknowledged as worshipping the same God, but failing to recognize His Son, they were barely tolerated and only not genocided specifically because they were considered slightly more trustworthy than Muslims, who got a bad rap because (Muslim) Moroccan raiders were hitting coasts from Italy all the way up to the Scandes. Comparatively, there was
no Jewish state in a position to start shit.
So there is this class of insular wealthy people, who seemingly only exist to lend money at extortionate rates and pounce like vultures at the slightest misfortune. Actually, just watch a production of
The Merchant of Venice to see the perception of Jews at the time. For those who haven't seen it...
- Shylock is a little bitch who loves money. All Antonio's homies hate Shylock.
- When he loses his money, he gets spiteful and wants to get his "pound of flesh".
- As a Jew, he's on the hook for attempted murder of a Christian, and in his status of an outsider, he's all set to get the death penalty.
- His "deal" featuring forced conversion to Christianity and confiscation of his worldly possessions is meant to be Antonio trying to save his soul in spite of everything.
Jews were often expelled once the realm was indebted to Jewish families. As usury was a sin in Catholic teachings, their wealth had been acquired via sin
anyway and a sovereign's confiscation of it was simply justice, don't let the door hit you on the way out.
The sovereign was going to confiscate the wealth of anyone doing that anyway, the Jews already conveniently otherized themselves, so it was a slam dunk.
And that is how we get to the number of 109, 109 times, specific Jewish families and institutions overreached and got slapped the fuck down by feudal realms in Medieval Europe. Other nations that supposedly banned Jews would just straight-up force them to convert at the point of a sword or assign them legal status as "dhimmi", which basically translates to "you pay protection money that only protects you from the authorities, all other soldiers of Islam (i.e. adherents not in the military) can still kill you and loot your stuff, facing little to no consequences, but we're not sending the army to kill you". The Third Reich only got as far as it did because of years of communist
freikorps pretty much owning the streets with ((Jewish)) shops (manifestations of capitalism) being left untouched long enough for the Nazis to break in and loot them during Kristallnacht, among the other excesses of a wealthy insulated class. One can equate Jews to the French nobility compared to the peasantry around the time of the Revolution,
all the time.