Bigger vehicles are "trucks" and smaller vehicles are "cars". They have different standards. So while a small Japanese truck may have more efficient than a larger truck, it is legally a very inefficient car.
This is also why SUVs exist, they are legally trucks for fuel efficiency/etc.
These Stupid Trucks are Literally Killing Us [1] explains in detail how "trucks" overtook "cars" as the most popular vehicle in the US, and legislation that lead to that.
(Quotes because the words refer to the legal definition of trucks/cars.)
I read an article recently about the growth in sales of such "trucks" in Australia. In there people were complaining that the existing parking spaces aren't big enough for these vehicles, so there should be a review into parking regulations to make spots bigger to accommodate them.
In my mind I would like to see the opposite happen, and instead have a review into these "trucks" to see if they are actually what we want for the road.
There's been diagrams produced that through the ages these vehicles have been getting bigger but with less actual cargo space in them. While some in the country might want them I don't believe for a moment they are as necessary nor as useful for the cities and suburbs where parking space sizes would matter.
I have seen some of them prevent people from fueling their vehicles at local service stations. The current sizes are not compatible with size expectations.
I want to say there was a Ford which had a fuel port on the rear of the vehicle which had to position the car further forward than usual, blocking the traffic exit while filing up the vehicle.
This is also why SUVs exist, they are legally trucks for fuel efficiency/etc.