What drove the form the economic policies took was the fact that Nkrumah needed to use them to buy political support and sustain his undemocratic regime.
But why is the ignorance hypothesis wrong in the core of it? It is all mainly because of the market failure and the difference of explaining it is just the intent of the policies. In some examples, it is about the circumstances which made them take those decisions but still don't get why it is not a efficient way to explain.