At 48 volts you start running engine accessories off of the electrical bus instead of belts and pulleys. That means the engine isn't necessarily responsible for keeping everything under the hood running at all times. You might not need a water pump or the AC when the engine is off, except to keep the cabin comfortable. But you still need things like power steering and power brakes, stability control and other safety systems.

Also, you start getting economies of scale with all-electric car components that pull down the price of EVs over time, because they can use the same components.