The govt definitely can identify the owner of the car based on the license plate.
Oh sure, cars are totally captured by government. But electronics are not completely yet, and if you want to be able to use electronics to enable independent communications or independent economical transfers, they need to stay outside the grasp of government. And besides government, having suppliers be able to capture serial numbers and tie them to specific hardware is just another possible angle of attack. It's a small thing, but small things add up on the longer term.