Communism101

Historically, the vast majority of people were de facto small landholder subsistence farmers. It is not unusual for people with a "foreign" culture to be dispossessed of their land, and such people either move to the cities (where you don't need to own land to support yourself) or leave for a "home country". Or in the case of the Roma, adopt a nomadic lifestyle, but that's beyond the scope of your question.

Under the Medievalist mode of production (which existed in some form until the early 1900s in much of Europe), consolation and profit-seeking are not present the way they are under Capitalism. Peasants farm enough that they can feed their families, pay their taxes, and sell a little bit on the market to buy what manufactured goods they desire that they cannot make at home; despite owning land (sometimes quite a bit of it!), they tend to remain relatively poor.

However, in cities, there was more potential for a common person to consolidate wealth and power through trade, banking, and professional jobs (lawyering, doctoring, etc.), as well as primitive ownership of the means of production (in this time period, often Mines and urban real estate, since agricultural land was still the purview of nobles and peasants). Especially if those common people were part of a relatively insular community within the city that fostered a culture of brotherhood and helping each other, as well as a culture of excelling in these urban positions since they were fully dissociated from agricultural production because of their race. Especially before the Reformation, Jewish people also excelled at these roles because of Catholic prohibitions against usury and a general disdain for the private accumulation of wealth.

Antisemitism stems from a broader trend in the time of disdain towards city folk - as opposed to peasants who were morally upright, content, and loyal to the crown, city folk were seen as morally loose, greedy, and harboring radical ideas. The Jews receive a special element of hatred for being "different" in a distinctive way, and when they achieve high positions in professional and bourgeois circles, gentiles see this as a threat - upstarts taking what is rightfully theirs.