I make ISK from my industry, by mining my own minerals, my reprocessing skill makes it, so that i make a small profit by reprocessing compared to selling ores / buying materials.
i have the entire production chain from ores to finished product.
each step increases the “worth” of the minerals i put into it.
i might only make a “pure profit” of maybe 0.5 isk pr unit of material i put into a ship, but when you put maybe 30 million units of material into a ship, you have increased your profit by 15 mill, before you sell the ship for another profit.