It's only 50% lower because most electricity grids emit a lot of carbon. Once the grid switches to 100% carbon-free, the number becomes a lot lower. And most of the embodied carbon in the car comes from industrial electricity or transport, so as the grid & transport goes green the embodied carbon goes down, eventually to zero.

Electricity only accounts for about 25% of greenhouse gas emissions, but it also enables industry (20%) and transportation (15%) to decarbonize too, by allowing them to replace their fuel with electricity.

A 50% reduction is already massive, but electrification of both vehicles and the industrial processes creating the vehicle will eventually let that number go to zero which should be our goal.