South Africa is not the most developed country in Africa. My friend, do your research properly. There are so many economic reasons for slums to grow. Slums indicates the presence of high unemployment, poverty, social conflicts and economic stagnation, to mention a few. What does that tell us about Kenya and South Africa? It tells us that their economies are not that strong to tackle problems of poverty, development of public housing and slums upgrading.
Strong economies do not have slums for they can afford to eradicate it. As I said, slums indicate poor economic growth, Tanzania has no slums compared to kenya and its economy is growing faster than Kenya. Research shows that in 2030, people living in slums in Kenya will double due to reasons indicated above.