You asked a very reasonable question and honestly, it's what has become a norm that most poor people have a greater number of children than their richer counterparts but I must add that the approach you used in making your analysis is quite shallow and not fact-based.
what makes Africans have on average 8 kids while living in literal famine?
Even though most African countries are underdeveloped and are mostly looked at on the global stage as being dominated by poverty-stricken families, in reality, that's far from what's actually the case. As a core African man who has lived both in the village part of my country and the town, I can boldly say that it's not true that we've witnessed anything close to feminine except in war zones where people can't comfortably go out to carry out their daily hustle.
The mentality of most poor people in the locality is that with more children, you have more hands that can help you on your farm, and that can also help you when you're old and that's the reason why they normally have more children compared to the richer folks.
Religion also plays its own role in this matter cause for some religions, you can marry as many wives as you find comfortable with, and for each of the wives you've married, they will expect to have a child for you and by so doing, you find out that some men might get married to 6 wives and have at least 3 kids from each of them. For this scenario, you can't say it's about wealth cause most of the people who marry too many wives are mostly traditional people who aren't rich in Their context.
do there brains cannot comprehend the future or something? are they that stupid?
Individuals' projection of the future varies and while some will dime it fit that they will only give birth to children they can feed and take care of their education, others might term it a thing of pride that they have so many children who will grow up to take care of them in the future.
Again another factor that even plays a greater role could be education and for most cases, educated people tend to have a lesser number of children than uneducated ones due to their general perception of a child's training.
There are more than a thousand and one reasons why people decide to have more children and poverty is just one of them.