Genetically modified crops were developed primarily to resist herbicides and pesticides, not to increase yield or nutrition. The original purpose was chemical tolerance, a fact often misunderstood in debates about GMO foods.
When we started to genetically modify food organisms, we did so so that we could make this seed resistant to glyphosate, to actually insecticides, to pesticides, to herbicides, to make it resistant to certain poisons. We didn't do it to enhance the crop yield. We didn't do it so we could enhance the nutritional content of the food. We did it purely so that we could enhance the yield of the crop by allowing it to be resistant to B phosphates or poisons.
