Might be for transformers windings in vs windings out? I think transformers are pretty efficient, but convert voltage in multiples. I'm not an EE though and don't know if that is how electrical conversion is actually handled in cars.
Transformers only apply to AC, where there is a fluctuating magnetic field.
A transformer in a DC circuit is just a physically large (very low resistance) resistor.
The standard practice to convert DC voltage (at least for these voltages) would be a buck converter, which is an active circuit. [1]