I mean, it's a bit overly broad of an analogy. Iron can't be manufactured on demand either. Neither can corn.

Corn can be, and regularly is; iron is abundant. Both are priced by their functionality (with a price floor set by the cost of manufacturing/extracting/growing if we ignore subsidies for a moment). If they become too expensive, they will be replaced by other cheap metals or crop in most uses.

Gold/bitcoins/diamonds just become more desirable when their price goes up.