This makes no sense.
Smart charging: you get home from work at 6pm after your 50 mile commute, and plug your car in to your 7kW home charger. You've used 15kWh of power that day. You're set to leave again at 8am. The car could recharge in around 2 hours. But demand for electricity is high between 6pm and 8pm. And the car has 14 hours to recharge. So charging can wait until demand has fallen, and then proceed at a slower rate overnight, with the charge rate mirroring the amount of surplus electricity.
Why does this require that cars are plugged in at every opportunity?
It's millions of people plugging in at the same time which is the issue. It causes a huge spike.