I believe, there are 2 reasons for that: 1) there are some problems in Africa that can be solved with Bitcoin, such as remittances 2) MMM, obviously
And it also allows many Africans to make money, you know. If they are able to buy Bitcoins on exchanges, they can later sell them to other people at a higher exchange rate for ZAR.
Makes sense they google about that and create websites on where to buy Bitcoins, such as this one.
So, everyone tries to do business in this world