In a nutshell due to several things in concurrence;
1.) Tribalism is still very much alive and well in Africa, not unlike it was a couple hundred years ago in Ireland and Scotland.
2.)Despotism/and Nepotism, which again is usually tribally based. Remember when Mobutu used funds given to him for developing Congo's infrastrcture to build a modern, 8 lane expressway in Kinshasa from the Capitol building to his house? --Which by the way, his motorcade was the only thing allowed on it.
3.) Entrenched corruption.See above, but also, instead of developing their own technologies and own businessess, The people in control of Africa find it more profitable in the short term to hire outside contractors from more developed countries to extract the rescources of their countries. -- In short, they are greedy and only concerned for themselves, their families, and larger clans, not the common good of all people in their countries.
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When There's No There to get to, I'm so There!