And? This is a game. Africa is supposed to feel different than Southeast Asia and utilize different systems, hence they utilize this one. Sokoto is there as an abstraction for other states, the Zulus because, well, people might want to play as them! Unless a different system of interaction with other countries is developed, adding more countries there serves no purpose.
Yeah it's a game but it's a game set in 1836. And part of the charm of Paradox's games is that you play in a historically accurate setting and can choose to be any country in the world. Africa is a part of the world and despite what most high school history courses teach, it had a lot of countries in it during the 19th century. It wasn't just a mass of undifferentiated natives whose sole purpose was to regulate the speed of colonial expansion.
I know a forum post isn't going to change anything for Vicky 2 at this point, but I hope next time Paradox makes a game they keep in mind that there is more to the world than Europe. They should be trying to find a fun way to model Africa realistically.