Interesting point! Archers' daggers...
Contrary to popular fantasy, most people were armed with more mundane weapons - simple spears, shields, smaller swords, and missile weapons. I've read somewhere that many African armies in that region used mostly archers with poisoned arrows. The chance of an archer needing to fight close-in was probably rarer than say a warrior armed with a club, sword, or spear - but if caught close-in had to be able to deploy his close-range weapon quickly... thus the loop dagger, very cool.
Was this loop-dagger style unique to that region or did this innovation find appeal in other parts of Africa?