It doesn't take hoarding, although that doesn't help. There are precious few products that can stay on the shelves when everyone decides they need some at once.

At northern latitudes, there isn't an available amount of sunlight, such that dark-skinned people can synthesize a healthy amount of vitamin D. Indeed, this is probably why light skin is selected for at those latitudes.

As a silver lining, I hope this crisis will provoke awareness of that fact. In most parts of the US, people with dark skin should definitely be taking supplemental Vitamin D. Really everyone should, unless they're a light-skinned sun-worshipper living in the Sun Belt.