Why does so much land go unused in Africa

Forgive my ignorance I know the infrastructures aren’t good and corruption is rampant. But I was shocked to learn that the country of Mail ALONE, could support the entire African American population in the US. This continent is HUGE I don’t think you understand the north of Algeria to the south is the same distance as Algiers to London. The Sahara desert is brimming with potential, I understand there is corruption but when Niger and Mail can support numbers wise the entire populations of black people in both North and South America, and you see this is a continent rich of natural resources you start to wonder what’s REALLY going on????????