. One advantage of the 6 volt systems used in cars through the early to mid 1950s was that the wiring was a thicker gage and could carry more current than the wiring on the later 12 volt systems.
Funny how perspectives change over time. The reason they went to higher voltage was to reduce the necessary wiring gauge and therefore reduce the cost. Power is power. If you need to supply 1200 watts, there are many ways to slice the egg. Do the math and you may discover the old wire gauge was insufficient for that amount of power even though they had a penchant for over-designing things back then.