One other advantage of the 12 volt system was getting all automakers on the same page with voltage and eventually polarity. Some vehicles were positive ground while others were negative. Some 6 volt while others 12 volt.
Another advantage with 12 volts was they could use smaller diameter wire to do the work. Saves a little money on buying wiring for vehicles if the wires are smaller.
At one time some vehicle manufacturers were talking about going to 48 volts because they could make the wire for various systems even smaller and save weight on the vehicle as well as having to use less copper for the wire. So far it seems that idea was scrapped.
