Africa is 50 something countries and hundreds of operators. Whilst it would be fair to say that overall the risk of flying in Africa is higher than in Western Europe or North America, if you look at individual countries you will find a huge variance, such as that between, for example, DRC and South Africa, the latter being possibly one of the safest countries in the world in which to fly.
welliewanger's post gives you some good answers. I'd add to the negatives, poor or often non existent ATC over much of the continent.
Safety will not be improved until there is money to throw at it. Most of the governments in Africa are so corrupt that any money thrown at the problems will end up in the Swiss bank accounts of the despots who are in 'power'.