It's quite true that all life started in Africa and it's also true that the cradle of civilization or at least one of them was Egypt as well as the first world power, but just because life started in Africa doesn't mean that civilization continued through out Africa.

The Egyptians where known to have ties with the Romans and not really with other African nations, so you can't really say that them being in Africa was supposed to lead to the development of the continent.

Further more, the continent is rich in numerous mineral resources and this made Africa a hotspot for foreign invasion and exploitation. The likes of King Leopold II were amongst the first to completely and utterly rape the African continent of its mineral, particularly ivory and rubber, resulting in the deaths of millions of Africans, mainly the Congolese.

He was one of the forefathers of African colonialism and set the continent down a path which it could never return from. Other countries like France and England aswell also joined in and took all they could from the continent. By the time they were done, the continent was laid bare, and unable to recover.