You are using circular reasoning in your logic, you assume the premise is true and from there you derive your evidence.
I would contend that someone thought about it and decided to go with the cheaper option because they could get away with it. I would consider my assumption to have more grounding given my experience with manufacturing and cost accounting.
My example of weights is that the steel weighs are cheaper than the alternative of using heavier drivers, by adding weight they are signaling premium without delivering it. Similarly with the USB cable, consumers assume such cables are thick because of thicker wires and better shielding, it’s cheaper to make a thick cable without those those features, once again signaling premium without actually providing it.
The vast majority of high volume consumer manufacturers use cost accounting practices which would absolutely be tracking and attributing the usb cable costs and the whole point of that accounting practice is to constantly be thinking about minimizing costs of even the smallest inputs, all the way down to the individual screws used. Yes, they’re thinking about how to save 1/100ths of a cent from each screw.