I think they use standard wiring harnesses for various models. It reduces inventory and the chance for installing the wrong harness. In big manufacturing, that little bit of wire, terminals and connectors is a negligible cost. It saves time and inventory space and simplifies the logistics of getting the right part to the right vehicle at exactly the right time. In today's manufacturing world, parts for vehicles are delivered right when they are needed. There is no stockpile of parts at the plant waiting to be installed. At the BMW plant where I work, many parts are installed in vehicles within minutes or hours of coming off the delivery trucks from nearby suppliers. It's an amazing process to watch.
Many rangers have fog light wiring installed even if they don't have fog lights. Some of the power door lock/power windows wiring is also installed.