Most of Africa is impossible to traverse internally. In addition, you have 2000 of the world's 3000 languages there. With a total of 8000 dialects.In Europe linguistic diversity may have been limited with many languages being driven to extinction. Empires in Europe were often assimilationist.
Those are a few theories. As for African scholars they existed in pockets. Also, one of the oldest universities in the world is in Sankore in Timbuktu. Books were more a currency there than gold, at one point. Let's not forget they had a golden age as well. As a Muslim maybe you should consider reading up.