The answer is partly in the story...microenterprise loans that immigrants get, to help them become productive Americans. But it's also that they band together and pool resources. That's why there are so many immigrant-owned convenience stores and motels.
Interestingly, despite the huge take on cigarette-smuggling operations (small fry like the Mauritanians rely on the Arab distribution network, but even the big Chinese syndicates do, somewhat), they live in squalor while sending multimillions over to terror groups.
Source: my brother is a detective who focuses on these cases.