Until recently no one has bothered to invest in Africa
What is "recent" ? Western powers were kept out for a long time because of malaria. Once that was controlled, the British invested heavily. But lack of reliable local labour forced then to bring in large numbers of Indian and Chinese, as well as Europeans, to get anything done. You cannot do that now, plus there are massive barriers with the local bureaucracy. Just getting spare parts into the country is extremely slow, even with bribes.