Why is the lingua franca of many parts of east africa not an indigenous language?

This is because many parts of east Africa have been historically colonized by the United Kingdom and France. This is why English and French are spoken in these parts of Africa today, instead of an indigenous African language. These areas have been under British and French rule for a long time so those languages tended to stick with the people. 

It's considered to be association or connection

Iwould say all the above personally but i think the desert would be d