For many of us in the USA, you're assumption about what we care about is bullshit wrong.
I live in Portland, Oregon. If I'm going north or south, I'm sometimes interested in mpg, but it isn't a big thing. Never very far from an Interstate highway in those directions.
But if I'm going northeast or southwest, mpg is critical, because there are too many back roads in the Washington and Oregon outback where running out of gas would put one in serious danger, and not be just a bit of an inconvenience. Having to hike 50 miles to the nearest gas station in the summer heat with no water or shade to be found is something to avoid.
This is not unique to Oregon. There are a lot of places throughout the USA where people often drive into what passes these days for wilderness, where if you don't estimate how many miles you've got left in the tank, you could end up in an unhealthy or even deadly experience.
MPG is the sensible measure to use in North America. Perhaps someday that will become kpl, but it will never make sense to use gallons per mile or kilometers per liter.
Now fuel for construction equipment that might travel all of 10 miles in an 8 hour shift needs to be measured in gallons per hour, but that's an entirely different thing.