Personally , I think the two main reasons why Africa is poor are corruption and political instability.
Corruption and political instability go hand in hand and are at the root of poverty in poor countries, not just Africa. This is basic knowledge and the OP also made it clear that "corruption" is not an explanation he needs to know because it's something that no one doesn't know. What he wanted to know was the underlying cause behind it all?
Yeah, basic knowledge doesn't cut it when we're talking about centuries of people being taken advantage of. And how money and power still aren't distributed equally worldwide. Colonialism directly robbed those countries and their people. And these systems are still messing them over today, stealing resources and rigging economics so the rich get richer. It isn't just about some bad leader being corrupt or unstable. This whole thing is bigger than that.