Underdeveloped by centuries of slave trading, mineral theft, social oppression and political repression under colonial rule, traditional tribal boundaries erased and arbitrarily drawn up borders imposed by Europe, puppet leaders installed as satellite Communist fighters, good politicians murdered, corrupt politicians steal from the people, sweetheart deals for multinational firms with no ethics, superstition and ignorance allowing disease to flourish, religious and tribal warfare, failed states, power vacuums and not much hope that things will get better.
In fairness, there is a legitimate middle class in parts of Africa, but by and large, it's a basket case.