I know that those places did write stuff down, but apparently the vast majority of sources come from Arab travellers. For instance, there this civil war between Mansa Musa's brother and his queen that we only know about because Ibn Battuta was there to see it. Similarly, according to Wikipedia we don't know much about why Kush broke up, and don't know much about the fall of its descendant kingdom Alodia either.
On mobile. Both wrote plenty, the nubian script has yet to be deciphered and there is a great deal of manuscripts written by west african states. Some places to start would be recent texts by Michael Gomez African Dominion and Bruce Hall the history of race in west Africa. If you are interested in Medieval of African states, Ethiopia also has a great deal of writings, many of them have been translated into European languages. In terms of histories of this state, Tadesse Tamrat's Church and State is still the canonical survey. I think that this issue is that in the West we are socialized that Africans and by extension Black people act differently than other groups and it never gets corrected. I was lecturing on Ethiopia and was talking about the castles built in Gondar, and my students did not believe me, I had to go to my office and show them a picture of me in a castle in Ethiopia.