Why did two factories quote the same style so differently?

Four things usually differ, and only one of them is price. The fabric actually specified may not match on weight, composition or stretch recovery. The construction may be different. What the quote includes may differ, because testing, packaging, inland freight and export documents are often left out by one side and included by the other. And the two factories probably assumed different order quantities.

Before comparing numbers, send both the same tech pack, the same quantity per colour and the same Incoterm, then ask each to break the price into the six blocks. When the blocks sit side by side the real difference is visible in one line.