Many of them work the carnival/fair circuit in America to get away from their own country.
I lived and worked with three white South Africans in Key West in 1992. They knew what was going to happen and were working here illegally, afraid to go back. There were hundreds of South Africans working in Key West back then, usually in the cheesy shirt shops.
Actually, many of the farmers from South Africa work as cheap hired hands on farms here (the growing seasons are opposite of those below the equator) and make enough money to hire other people in South Africa to take care of their own farms as hired hands, and then those smaller farmers in turn hire Zimbabweans to run their farms. Nobody farms in Zimbabwe; it's too dangerous.