I think the banking/Jews connection may be a bit more of a special case. I can think of lots of theories about why it seems to happen; when a population is very small (e.g., black people in 18th century rural England) no one has got as far as forming rigid opinions about what they should/should not do; the fact that "political correctness" applied mindlessly can be as rigid and constraining as good old fashioned stereotyping; the effect of rising population/wealth/middle class on the choices available to both employers and employees and the extent to which women, for instance, could remain at home rather than having to go out to work to feed the family; the way ideas of social justice play out (e.g., the successful campaign to curtail the "heinous" practice of women being employed by the pit); the rise of the commercial mass-market entertainment industry; and so on. Since I'm not a sociologist I have no idea which, if any, of the above actually come into play.