Why did so many post-colonial African nations end up with bad leaders?

To use the extreme case of the Democratic Republic of the Congo which gained its independence from Belgium on 30th June 1960: education of the local population was conducted on such a limited scale that the first native college graduate graduated in 1956 and by independence there were only fourteen non-european college graduates in the country from which to draw the leadership of the new nation. The political and economic administration of the Belgian Congo was undertaken by a Trinity of state, missionary and commercial interests and these entities and their personnel were by and large withdrawn as a result of the end of colonial rule as part of a deliberate policy of non-cooperation with the new government, thereby denying the new state any expertise in management or government during the transitional period. Ideological differences, factionalism and competition for power between these individuals were encouraged and exacerbated by foreign powers and commercial interests seeking to maintain autonomous territorial enclaves for extractive industries like mining to keep them free from interference by the new government.

This small pool of potential leaders was further shrunk by death and imprisonment as armed conflict was fomented to destabilize the new state, in the case of the DRC its democratically elected leader Patrice Lumumba was kidnapped and brought to the breakaway Katanga region which was at that point administered by colonial era mining interests and executed by mercenary forces. This region exists to this day as a lawless haven for illicit resource extraction (often by slave labor with the profits supporting rebel groups) beyond the control of the DRC government and a key source of the rare earth minerals used in the consumer electronics revolution.

In many cases the existing pool of leadership talent was quite small, from there it was further attritted by factional conflict, personal rivalries and political violence both internally and externally instigated. In many cases the initial post independence leadership knew how to go about improving the circumstances of their nation but were unable to proceed against obstinately imbedded residual colonial interests. These interests involved the foreign policy establishments of their respective nations and as these new leaders searched for the aid and assistance that was often spitefully denied to them by their former colonial dominators they found themselves drawn into the cold war conflict for influence in the third world. In this new environment these new leaders often found themselves murdered by or dependent on the leaders of the armed groups warring in internal conflicts (not always instigated but almost always sustained by foreign powers) or mercenaries hired to fight them. Too often these nascent leaders found themselves imprisoned or murdered by the leaders of these armed groups who though often competent military leaders, proved to often be poorly educated and out of their depth in matters of civil administration. In this horrific catch 22 most of the qualified leadership talent found themselves marginalized or killed while the rest were left with the knowledge that asking abroad for help was just as likely to kick-start the foreign inspired machinations that would likely result in the termination of their leadership.

There are cultural and intellectual trends at work here which included among some a rejection of Westernism and the seeking of indigenous, African originated solutions to the questions and issues facing these new governments but that is beyond my expertise and for another poster.