The lack of eugenics.
The races that rose above the others rose from pain and suffering. Africans, on the other hand, never knew what pain and suffering were like back in the time.

1-There was more than enough animals, thus they didn't learned how to hoard.
2-Jungles with tens of millions of fruit trees, the fruit was rotting on the ground because no one picked it up and they didn't learn how to farm

The only thing they could ever do in their day is chuck their spears to hunt, nothing more, nothing less, but the colonialism really fucked them over.
White people brought new technology to the Africans, and this technology made their lives much easier and enojyable, which made their numbers grow. When the Whites first arrived in Africa, there were more animals than Blacks, as the African population didn't reach 100M back then. Africans never knew booz, tobacco, guns, or any luxury that white people invented or brought to them, and more importantly, they never knew why the Whites were giving them these things for some shiny rocks or toxic metals or anything that they never use yet they had it lying around everywhere

When the Whites left, Africans found their life easier, and they had new luxury things, but at the same time, they don't know how to create these things, and now their numbers have tripled, and the free resources Mother Nature used to give them aren't enough. That's why when the Whites left, the Africans starved to death (Zimbabwe is just an example), and now South Africa is on the way when they genocide the Boers.

Anyone who says slavery and exploitation is the reason is an idiot. Most nations on Earth have been enslaved at a certain time, and they do better than Africa after things get back to normal, not imdidtly but they didn't take an entire 100 years like the Africans.
The Celts under the Romans, the Levantines under the Persians, the Slavs under the Ottomans, the Native Americans under the Spanish, and the Anglos under the Norse, yet all these nations do better than the Africans before and now.
Africans either get their numbers back to less than 100M or pay the bill of the easy life their ancestors have enjoyed in such land.
Other than that, Africans have no other choice.