"Iodine levels of meat, chicken, eggs and dairy products are reflective of the iodine content of the animal feed used. The iodine content of vegetables, fruits and grains generally reflect the iodine level of the soil in which they were grown. The iodine content of New Zealand soils is low and therefore locally produced foods are also low in iodine. It is difficult for most people to obtain adequate iodine by eating foods that are natural sources of iodine, which is why commercially prepared bread must be fortified with iodine."

It's true you only need a small amount, but poor communities do not have access to rich sources of fresh food and sea salt has no iodine.