Has anyone ever tried to send a billionth of a bitcoin? Seriously. You can't, not with bitcoin-qt or bitcoin-core or whatever they are calling it these days.
Bitcoin is for RICH, relatively speaking, people, in the West and China. No real person wants to buy a fraction of a btc, only bots.
Africa is NOT ready for bitcoins. They are too busy fighting ebola, figuring out where their next meal is coming. Sure, some are using their phones for micro transactions, but they are too miniscule in amount to attract any real usage.
Africa has some of the fastest growing economies on the planet. Not everyone in Africa is poor, and even in the poorest parts everyone has cell phones. If someone could devise a way to make international bitcoin transfers possible with old fashioned cell phones with good security and useability, it could easily take off.