Final answer:
The difficulty in obtaining the cure for river blindness for those affected is primarily caused by economic factors, as the affected individuals or their countries do not have the economic resources to purchase the necessary medication.
Step-by-step explanation:
The cure for river blindness was difficult for the people impacted by the disease to primarily obtain due to economic factors. Those affected by illnesses like river blindness or AIDS in regions such as Africa and Southeast Asia often have limited access to treatments that are readily available in wealthier countries like the United States and Europe. This disparity is largely because the patients or the countries where they live lack the resources to purchase the necessary drugs. Economic constraints, therefore, play a crucial role in the availability of treatment for diseases in less affluent parts of the world.