@Moon Resource curse, when you have abundant resources you don't really need use them effectively and when someone who knows how to use the resources better comes along they easily beat you.
Also the political systems in Africa were always incentivized producting less because your extra stuff would just get stolen by bandits or your local warlord.
There's also that there are more illnesses in Africa and that there aren't animals that can be domesticated.
There are multiple causes to problems like this each contributing a different amount, but people who primarily blame the west are fucking retarded.