The salts cause the plants to bloat, just as excessive salt in human diets causes water retention and bloating. Furthermore, chemical fertilizers cause the death of soil microorganisms and break down soil structure, which in turn destroys the natural system of plant nutrition.
Fruits have larger plant cells because of water.
The application of more irrigation water can increase the size of some fruits and vegetables, and there is more money per pound gained with water-laden foods. Most organic producers apply less irrigation. Some conventionally grown crops are sprayed with chemicals that increase water uptake in cells, most notably grapes. These sprays are expensive, so it is not done on things like grain crops. Fruits are bigger by breeding.