Study engineering is more diffic. than business and management, but why average salary of a bus-man is higher?

I am not sure that I agree that engineering is more difficult than business and management, but salaries are based more on supply and demand than anything else. If there is less demand for engineers than business people, then salaries will be lower for the engineers. It could also have something to do with the area of study. For instance, there may be a need for Civil Engineers but not so much for Electrical Engineers or some other area of engineering. These things also seem to run in cycles. The cycle could turn the other way in a few years.