I would probably be growing the garden because (if I lived in that time period) my brother and my father would be fighting in the war and I would want to help somehow.
If I had a garden that means I could have food to feed my family and people in my town.
The purpose of victory gardens is to produce your own food during the war. This would provide food for you and your family. You would also be helping the war effort.
Most of the food that would usually be in stores would be going towards the war effort so everyone would have to make their own food.