Why Do Two Bag Factories Give Different Prices for the Same Design?

You send the same tote bag drawing to two factories. One quotes USD 3.20. Another quotes USD 5.80. At first, it feels like one of them must be wrong. Maybe the higher factory is overcharging. Maybe the lower factory is trying to win the order. But in real custom bag manufacturing, two factories can look at the same design and silently make very different assumptions about fabric weight, lining, zipper grade, logo process, sewing reinforcement, packaging, inspection, sample revisions, and export preparation.