Africa is relatively underpopulated compared to other continents. China alone has more people than all of Africa.
Africa is having a population of more than a billion, and its is the
second most populous continent after Asia. Comparing the Chinese with the Africans, you have to keep in mind that the Chinese doesn't depend on food aid from the developed nations, but more than 50% of the Africans are dependent on it. With the Western economies still in recession, I don't think that the food aid will flow infinitely.
Africa is relatively underpopulated compared to the amount of land and resources they have. A lot of African countries are badly governed that's all.
China did suffer a famine about half a century ago.
Food aid from the west will flow indefinitely because that is mostly a by product of your food subsidies which benefit your own farmers at home. Also food aid is a very very small amount compared to the size of your economies. In return you get substantial leverage in resource rich African countries. For example you mentioned the DRC. Coltan is used in smart phones. Where would Apple's famed 50% gross margins be if the essential components of smart phones were more expensive?