You do realize export duties are set to regulate the GDP and is in a direct relationship to the value of goods produced and sold domestically, right? And you realize that if it weren't for export duties many goods produced here in the US would devalue, and more importantly could effect the value of our currency?
Conversely, import duties, or tariffs, are put in place to control the flow of goods into our domestic market, as to not saturate or overwhelm consumers. It's also closely related to GDP and currency valuation. Not to be confused with Trump's, currency influence argument.
I get the impression your not up on economics. Or perhaps you're more familiar with 'old school' ways of thinking?