The Federal Gas Tax is one tax for the whole country. You try to raise that, and there is a political price to be paid. The state gas taxes are resistant to change, because local legislators know they will lose votes if they raise them.
But if there are a thousand little road use zones, each with it’s own tax rate, each rate can be raised, little by little, with hardly any objection from the taxpaying population.
So the per mile usage fee will increase exponentially, while the Gas Tax has stayed the same for years. The first person who expresses surprise when this happens should be put up against the wall.
Ribbet!