Fun fact all these rules act as contraception. Who wants to have a third child when you can’t actually squeeze three car seats into the back of a car.
But I don't buy it: https://www.jefftk.com/p/three-car-seats
I got anecdata of people shopping for gargantuan 3-row SUVs so they can accommodate the third child seat. Most people don’t seem to mind as it’s “only” a monthly payment. (Over 8 years it’s a fortune in interest let alone the actual cost of the vehicle but most people don’t think that far ahead)
Who the hell has kids nowadays at that age? Not many in the first world.