But it doesn't matter. The number of vehicles taken either way is negligible. In the old days, you had to change the miles/km speedometer to the other one when you took you car with you as you emigrated. Buying a charge adapter is easier.
Arguing about 120V is a red herring. Just about every US home has 240V service, most cars will charge at 240V not 120V.
Single phase vs three phase is the big reason for a difference between US and EU charger plugs though. Three phase is pretty uncommon in residential areas in the US but is common in many EU countries. Industrial customers in the US will often have three phase but it's pretty rare to see outside of that.