Whats an example of why low levels of iodine in your diet can cause goiters?

Low amounts of thyroxine (T4, one of the two thyroid hormones) in the blood, due to lack of dietary iodine to make them, gives rise to high levels of thyroid stimulating hormone TSH, which stimulates the thyroid gland to increase many biochemical processes; the cellular growth and proliferation can result in the characteristic swelling or hyperplasia of the thyroid gland, or goiter