I don't see that as the root of the problem but the result of the way independence was granted. In a matter of a century, these peoples were moved from basically tribal, agrarian societies into a framework of the modern nation-state of which they had no say on the mechanics of organization. From the 1950s through the 70s, they were rapidly cut loose from the outside organization principles and then given the worst curse Western society could have left them with --- the Socialist economic model as imposed by the “enlightened” bureaucratic and academic elites of London and Paris. Socialism, even in a Western culture where there is a basic respect for individual rights, the rule of law, and a concern for the welfare and property of others beyond immediate kin, breeds corruption and establishment of an anointed and self-perpetuating elite which will eventually bring even the most well established national cultures to their knees. (See France)
In African cultures, where family and tribal rights take precedence over any concept of national kinship --- where there is no history of private property or cultural acceptance of competing "tribes" that were cobbled together by European colonists into the artificial nation-states, socialism became more than just economically retarding and socially destructive as in old Europe, but totally disastrous to the future of non-Western cultural and economic institutions.
The Socialism imposed by the European colonial powers, by combining economic and political power in the zero-sum game, which was inevitable considering African culture, guaranteed disaster. It could have been different.
I take your point, and agree that this was a significant factor. Human cultures have selected various ways to organize their social interactions, their governance, and their economic structure. Some have been unsuccessful in their own right, but the really monumental failures have come from hybirds. Africa is perhaps the premier example.
There are something like 1500 different languages spoken in Africa. A few countries have just one, but some have hundreds.