I have heard this explained away in a quick sentence along the lines of "there were few ports or resources along the coast." I still find this surprising, given that dragging gold across the desert is really difficult and that the societies that West Africa was trading with had highly developed maritime technology and traditions. Why didn't the Arabs (or the Europeans, or the Egyptians for that matter) just sail down the coast of Africa, load up on gold, and sail back? It seems very strange to me.
Hey there,
Just to let you know, your question is fine, and we're letting it stand. However, you should be aware that questions framed as 'Why didn't X do Y' relatively often don't get an answer that meets our standards (in our experience as moderators). There are a few reasons for this. Firstly, it often can be difficult to prove the counterfactual: historians know much more about what happened than what might have happened. Secondly, 'why didn't X do Y' questions are sometimes phrased in an ahistorical way. It's worth remembering that people in the past couldn't see into the future, and they generally didn't have all the information we now have about their situations; things that look obvious now didn't necessarily look that way at the time.
If you end up not getting a response after a day or two, consider asking a new question focusing instead on why what happened did happen (rather than why what didn't happen didn't happen) - this kind of question is more likely to get a response in our experience. Hope this helps!