Clothing is handmade. It doesn't matter if it's luxury or from Shein; it's all handmade. Artisans can work tirelessly to make sure everything is stitched the exact same way but anything below that is made for the mass market. Those tend to be people paid nothing to work as fast as possible to make as many items as possible. In that environment, you're going to get a lot of inconsistency. The only tech that helps here is the sewing machine and using lasers to cut the pieces. Compare that to iPhones where there are a lot of industrial machines that are used to create each of the pieces paired with highly trained individuals helping assemble it. The iPhone is also a "luxury" good so they have a lot of QC whereas a shirt from Old Navy is cheap and as long as it "looks" correct then they'll sell it for $8.