This is the difference between a medieval fantasy world and a modern technological society.
There are no factories, machine tools, or assembly lines. No matter how skilled or at what level of forging master one is, the blacksmith must personally hammer each object on the anvil to make it, resulting in extremely limited production capacity.
Even for batch-produced standard equipment with fixed procedures, the forging speed can't be considered fast, and shortages are more frequent.
Once an order deviates from the template, requiring custom crafting or even innovative design, the blacksmith must invest considerable personal time.
In myths and legends, master dwarf blacksmiths may spend years by the furnace for a divine artifact.
Barn's skills certainly aren't on that level, and River Valley Town's nature made him accustomed to time allocation—mornings reserved for custom crafting and afternoons and evenings for forging ordinary equipment.
