You can only grow coffee around the equator, and most countries in that part of the globe are not rich enough and/or don't have strong industries... The transformation and the demand for the end product usually occurs where it is consumed.
It's the same with cacao, most of it comes from Côte d'Ivoire but most Ivoirian farmers don't even know what chocolate looks like.
The issue of processing makes perfect sense and should be the main cause. Both coffee and cocoa, after being processed, become very expensive for the producing countries. I found some information on the subject:
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Correct. Also b/c of the hot and humid climate, people in those areas seemingly refrain from high intake of coffee related products.
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