What is their financial system like? My guess is not very good. I think most of the gains are going to go to private investors, businesses, and other countries that can afford to invest in large projects.
The three big ones there actually have a respectable amount of listings (Egypt 833, South Africa 402, Nigeria 223)
I expect you would find that the biggest companies in most of Africa are either state owned mining and oil companies or western companies operating in Africa. I don't think they have many important publicly traded companies because their financial systems aren't well developed.