The growth of soy production, trade, and use is the result of a deliberate trade policy. In 1962, as result of the 'Dillan Round' of the GATT (the predecessor of the WTO), the US and Europe agreed on a ban on import taxes of oil-containing crops (like soy). At that time the US was the main exporter. The other side of the agreement was that Europe would be allowed to subsidise its production of grains. For European factory farmers, this meant access to cheap proteins (from imported soy) and cheap carbohydrates (from subsidised grains), the two ingredients of a fast growing piece of meat. The result was a boom of fodder imports, meat production and meat export (including dumping) to the rest of the world. This agreement from '62 is still valid, although now the big corporate South American soy producers are benefiting from it.
