Usually these flights rely almost 100% for 'southbound' revenue generated from oil/mineral extraction companies who want stuff and want it now (and in the good old days corrupt dictators wanting foie gras, champagne, caviar).
which is why esp. in Africa many routings are round-robbins staging back home via Kenya (veggies & flowers) or Uganda (fish, veggies) or Tanazania (fish & veggies).