In a production or manufacturing environment, Economy of scale is a simple concept that tells us that the larger the production run, the lower the per unit cost will be.
Think of it this way:
If I purchase component parts for 1000 units I pay my parts supplier x dollars per unit. If I purchase component parts for 10,000 units I might pay x- 10% dollars per unit.
The higher volume should mean lower handling costs per unit for your supplier, and also lower handling costs per unit for your receiving department and warehouse staff.
It costs me the same amount to issue a purchase order and pay my suppliers invoice if I order 1000 pieces or 10,000 pieces, so again, lower per unit cost.
Actual manufacturing production line set up costs are a major cost of production. It takes time to modify each production work station, set up tools and testing equipment, and assign workers to specific tasks. It may take several hours to set up a production line for a specific product. If I want to produce 1000 pieces I may keep my production line busy for 1 day to produce 1,000 pieces. Then I have to retool for the next new item on the production line. If I start a production run for 10,000 pieces I may not have to retool the production line for 10 days. That amounts to a significant cost savings.
When you add up all of the cost savings from a larger production run vs a smaller run, the savings might be significant. The manufacturer may elect to pass some of those cost savings along to their customer resulting in a lower product price.