It is about safety. Larger cars on the streets are more dangerous for the people living in the city.

Cars have been getting ridiculously large over the past decades because the only force acting upon carmakers is the desire of the car buyer.

If I’m buying a car, I obviously want the largest car I can afford and semi-reasonably fit where I’m going to be. This has many benefits for me, but a lot of negative externalites for everyone around me.

That is why policies need to discourage larger cars in many ways, to keep the average size in check, so to speak.