Not to mention when humanity transitioned to more urban living and a lot of people got fed on cheap grain based product with precious little else. Which was usually just one kind of grain too.In the history of pretty much every kind of vitamin and mineral deficiency, there are entire nations and peoples saying the exact same thing. Scurvy, rickets, beriberi, kakke, pellagra, you name it. A lot of the time the solution existed but the people in question refused to follow the advise or practices of foreigners, holding that their traditions and customs could not possibly be wrong.
Can't see whats wrong if everyone around you has the exact same problem.