No, it's not by design, but is the unfortunate consequence of our current userbase, who have more experience in expat related issues in North-America, Europe, Australia than Africa, South-America or Asia. As they ask and answer more around these regions, it will gather more and more people, who are interested in these topics, while regions like yours will not get enough views, meaning less people from your region is likely to find this site, and come here in case they have a question to ask, or answer.
However we do welcome any expat related questions, no matter what the originating or destination country is, and if you think you have a good question that is relevant to people living as an expatriate in Africa (or any other region we are not representing well enough), then feel free to ask. While it's not guaranteed it will be answered quickly, it will make others like you feel less intimated by the other questions, and probably are going to come here to ask and share their experiences, making the site cover a more broader userbase.
You can also help in making sure this site becomes an even better FAQ site for expatriates around the world: If you know about an issue you've faced as an expat, you can not only ask a new question, but using the "Answer your own question" button also answer it in one go. If you think the problem you've faced would help others, then feel free to do so (given both your question and answer meets our usual criterias).