Need to factor in the carbon cost of constructing a new vehicle vs running a less efficient one for longer. Disposal and possible recycling of old vehicles, also not free. Upgrades to the charging grid and construction of charging locations for all those new vehicles. Brakes and tires also cause significant pollution and are still an issue no matter the power unit of the car.

Then compare all that to building trams and light rail in metro areas instead of building cities to accommodate cars, roads and parking lots instead of humans.