The main reason why West Africa was not a settler colony is that the region was already densely populated by indigenous peoples. In contrast, North America, Australia, and New Zealand were largely empty when Europeans arrived, which made it possible for them to establish large-scale settlements.
Another reason why West Africa was not a settler colony is that the climate was not as conducive to European settlement. The region is hot and humid, and it is prone to diseases such as malaria and yellow fever. This made it difficult for Europeans to live in West Africa for long periods of time.
As a result of these factors, West Africa remained a region dominated by indigenous peoples throughout the colonial period. European powers did not attempt to displace the indigenous peoples, but instead focused on exploiting the region's resources and trading with its inhabitants.