It takes a pretty extreme iodine deficiency to end up with goiters. In most environments, there's enough in the soil that eating local plants / animals that eat those plants supplies enough.

The iodine deficiency issues that haunted the Swiss (and Appalachia) arose from people settling down from nomadic lifestyles, in mountainous regions that easily were leeched of iodine by rainfall, and then farming that already leeched soil until there wasn't any iodine left at all.