Here's a few stabs:
- general lack of education, so lack of anything above subsistence employment for most;
- corrupt governments / dictators, who siphon off (usually, natural resource wealth). Often helped by greedier "Western" organisations or governments;
(it's generally a quicker fix to dig / drill for something, than to invest in the factories, roads, offices etc that create better employment prospects; not to mention the schools and universities, and healthcare, to look after the prospective employees;
- due to corrupt governance, lack of investment in infrastructure and productive capital, meaning poor general standard of living;
- due to corrupt governance, lack of stable and "just" society, which disincentivises honest entrepreneurial spirit; this means that black market and criminal gangs are the easiest ways to drag oneself out of subsistence existence;
- subjugation of women, rendering half of the potential earning capacity off-limits;
- poor general conditions, corruption, lack of education etc, disincentivises both home-grown and foreign investment.
You missed one out:
- the Africans' predilection for having enormous families and relying on the Saint Bobs of this world to throw food at them.