It's human-made famine, often as a form of war or a byproduct of war.

Also, much of that aid has been syphoned off by dictators and corrupt officials, which in turn makes charitable organizations hesitate to give.

That said, the dictators and corrupt officials are only following the example of non-African corporations, who for more than a century have exploited Africa for its natural resource, and before that exploited Africa for its human slaves.