>>17841829
1. Because you're not looking at the countries as a whole, you're looking at nice pretty photos of the urban parts which were maintained by rich, foreign countries. 99% of the population does not live in the city and suffers not one bit if the city now looks worse. Picking the Congo for your example is particularly egregious. Here's a more representative picture of the average Congolese's life under benevolent European rule. (He didn't lose his hand in a farming accident.)
2. European dominance no longer required European rule, Europeans (really, Americans) just realized you can get the minerals without enduring dengue fever thanks to modern communication technology. Why waste all your money propping up a capital and an administrative class for the country when you can just coup anyone who touches your diamond mines and leave some local kleptocrat to handle day-to-day admin? Especially when having a visible presence invites visible resentment. If life in British Buranda is shit, the locals blame the British and try to chase them out. If life in independent Buranda is shit, the locals blame their president and try to chase him out. In the first case, European business might also be chased out with the British leaders - in the latter? Well, you have the CIA sit the new president down for an informal talk where you explain that he can steal all he likes, but if he values his brains in his head instead of coating a local wall, he won't touch whitey's stuff.