Why must perfectly competitve markets always deal in commodities?

Perfectly competitive markets deal in commodities because these markets require homogenous products, where goods are identical and interchangeable among suppliers. This uniformity ensures that no single seller can influence the market price, as consumers will always choose the lowest-priced option. Additionally, the ease of entry and exit for firms in perfectly competitive markets leads to a focus on standard products that can be produced at scale, reinforcing the commodity nature of the market.