It's just the combination of a number of traits that were selected for in the past. A Jew who isn't hostile to the host society will eventually outmarry or convert. If the host society isn't weakened and undermined, it will identify and expel hostile groups. Given the pattern of expulsion and migration, short-term exploitation becomes very lucrative, with its upsides maximized and its downsides minimized.
Similar evolutionary pressures to a disease, really. Reduce the host's ability to defend itself and convert as much of its resources as possible into your resources. The health of a host isn't a major concern, since it's only temporary.