The French West Africa heritage flag is for the nations that were once a part of the superstate of Africa that existed from 1895-1958. The official flag was a French Flag, but in order to distinguish this entity from France this flag enables one to do so. France was able to weave the French language and Catholic Church deep into the fabric of these nations. Its only fitting that they have a unique flag that honors France and honors Africa.
Why a heritage flag? Well the official flag was the flag of France. Many bad events and many good event occurred due to French "adoption". In the end it is more so for the respect of French West African heritage, whose identity is now perpetually tied to France.