Why do some West African countries adopt the Unitary" system of government while others do not?

Why Some West African Countries Adopt the Unitary System While Others Do Not

A unitary system is one in which all governmental powers are concentrated in a single central government, while a federal system shares powers between a central government and component (regional/state) units. The choice between them depends on the peculiar conditions of each country.

Reasons some West African countries adopt the unitary system:

1. Small size of the country: Countries with small land area, such as The Gambia, Togo or Sierra Leone, can be conveniently governed from one centre.
2. Homogeneous population: Where the people share a common language, culture and religion, there is less need to divide power among diverse groups, so a single government suffices.
3. Desire for national unity: A strong central government is seen as a way of promoting unity and preventing division and secession.
4. Economic considerations: A unitary system is cheaper to run because it avoids the duplication of governmental structures found in a federation.
5. Ease and speed of administration: Concentrating power at the centre allows quick decision-making and uniform policies throughout the country.
6. Small and manageable population: A smaller population is easier to govern from a single centre.

Reasons others do not (they adopt federalism):

1. Large size: Large countries such as Nigeria are difficult to govern from one centre and need regional units.
2. Heterogeneous/plural society: The presence of many ethnic groups, languages, religions and cultures makes it necessary to share power and give each group a sense of belonging.
3. Fear of domination: Minority groups prefer federalism to protect themselves from domination by a single central power.
4. Historical background: Some states were formed by joining together formerly separate units that wished to retain some autonomy.
5. Uneven development: Wide differences in the level of development among regions favour a system that allows regional self-management.

(Any relevant points are acceptable.)