The work permit is only part of the equation. 

For an employer to employ someone with a general work permit the following applies according to 
http://southafrica.smetoolkit.org/sa/en/content/en/57344/Hiring-foreign-employees-–-a-guide-for-South-African-employers

"General Work Visa
The General work visa is issued to a foreign employee who has obtained a position with a SA company. The visa will only be issued if the employer demonstrates that national job recruitment efforts in the local media were fruitless..."

This process is arduous and can take manymonths to conclude. Not many employers are able to wait while these processes are complied with, leading them not to consider foreign nationals.

Scarce skills visas require ..."The applicant must demonstrate that they have said critical skills such as holding an advanced degree or publications in their field. They must register with the specialized SA professional group..."

Dispelling the myth that foreigners are taking local's job!