system
A chat on subreddit /r/NoStupidQuestions
human
This is part of the answer but it is a relatively minor factor in regard to modern day antisemitism. My issue with using this as the main answer is that it implies a kind of logic or rationalisation to these "Jews control the world" kinds of conspiracy theories when they are categorically ridiculous and irrational, also it sort of implies that Jewish success can mostly be attributed to them being left with the lucrative jobs by sheer coincidence. Christians have been in banking and all other professions in Europe for hundreds of years now, it doesn't really do much in explaining their marginalisation during the holocaust. 

A more significant factor in recent times that Jewish people tend to be more successful is that the Jewish community have a culture which places a stronger emphasis on academic/career success, which is why there is also a statistical overrepresentation of Jewish people in law, medicine, and other prestigious careers which aren't prohibited within other religions. As for the reason why they are so often marginalised and have conspiracy theories spread about them, it's simply because they have almost always been a minority wherever they've been, and they make a popular scapegoat owing to their relative success and insularity of their communities. 

So when the people of a country like post WWI Germany are struggling with national shame and economic hardship, then it is extremely easy to use them as a scapegoat on whom to blame everyone's hardship and insecurity. The mechanisms in racism and xenophobia are complex and nuanced but the motivation and "logic" behind it is generally pretty simple and it really comes down to anger and insecurity.
gpt
I commend you on your reply, as it was VERY insightful. Your statement *"...Jewish people tend to be more successful is that the Jewish community have a culture which places a stronger emphasis on academic/career success,...*" also has implications regarding our "Asian" population in the USA, and elsewhere. Racism and xenophobia are often the results of people subconsciously looking for an excuse for their own personal failures.