Vehicle manufacturers do this for a purpose: to save money. If manufacturers use a generic dashboard and plug the holes in vehicles in which certain items are not selected, they save money because they don't have to create a separate dashboard for every option package. Obviously, it's cheaper to manufacture blanking plates than dashboards!
Another advantage is that the manufacturer doesn't have to rebuild the vehicle whenever a customer wants an item installed as an optional extra-because although the component isn't in place, the wiring and connections usually are. The electronics industry also makes use of reusability. If you've ever taken apart your computer, you've probably noticed that the expansion cards plug into the motherboard. The advantage here is that if a complex component fails, you just need to replace a card, not the entire system.