Explain, IN FULL/COMPLETE DETAIL, all of the steps it takes to get a visa in RSA. And no, you aren't going to find that info on line. ;^)
South African citizens can apply for a visa at the US Embassy or Consulate and if they can afford an airline ticket, they can leave the country.
I have seen no source that would indicate that South African citizens are being forced by their government to remain in their country.