Because West is stealing gazillion times more from Africa in return. When you refuse, war and/or sanctions follow to cripple your country. Then they can loot in peace. You seriously think USA is just helping out of their good hearts?
The reality is far bleaker---but also more hopeful: rich countries don't benefit from (causing) bad conditions in poor countries, at least nearly not as much as the bad conditions cost the poor countries.
'The best time to buy is when there is blood on the streets' - Baron Rothschild.
India also got more investments since the liberalisation in the 90s (https://en.wikipedia.org/wiki/Economic_liberalisation_in_Ind...).
(I know less about Africa---but I suspect relatively stable and rich South Africa gets the lion's share of investments?)
Which instabilities are profitable to rich countries?
South Africa is very a profitable country to the West, not the other way round. It was even more profitable during the dark days of apartheid. That's why USA was sponsoring apartheid government with intelligence and arms. Google about Mandela arrest and CIA's involvement. They even listed Nelson Mandela as a terrorist. Even when he was President, he was still listed as a terrorist. US only removed him from the terrorist list few years ago.
I live in South Africa.