Manufacturers and retailers in the North have high costs. They invest in smart machinery and marketing. They pay high wages. It's only because people in the North are affluent that they can afford to spend their money on all that expensive coffee. In the South, on the other hand, costs are low.
Labour is cheap and there are no machines to pay for.
If coffee farmers made a better living other poor people would want to join them, too much coffee would then be produced, prices would fall and market forces would duly reassert themselves, taking us back to where we began. A perverse variant of this explanation informs the 'structural adjustment' policies that have been enforced throughout the South, including Peru, by the world's financial establishment. Because Southern societies are poor and in debt to the North they must cut government spending on things like education and health, 'privatize' everything and export more commodities like coffee. In this way the supply is increased, prices are reduced - and producers are impoverished. So the rich in the North are rich because they are rich, the poor in the South are poor because they are poor.