In fact in the UK you would be forced to aggregate all fuel and road tax and offset it against road maintenance because there is no direct correlation to be made, as tax is “one big bucket”.
The majority of the planet are going from one point of interest to another at a relative constant rate- but yes people are spread further and further- ironically this is helped by requiring huge parking space everywhere anyone needs to go, and needing huge houses so you can park multiple cars outside. Its a self-reinforcing problem.
(This is most evident when comparing cities like Malmö in Sweden with Orlando, FL. Malmö has a higher total population but approximately 1/20th the road surface- yet in Orlando I kept bumping into the same people everywhere I went because we’d all drive to the same Restaurants and Shops; and despite that happening we had to drive 20-25 minutes to get there! Weird coincidence or natural concentration points? Someone smarter than me would have to say).
Just to be clear, there's no specific "road tax" in the UK - it was abolished in 1937. Instead general taxation (e.g. income tax) pays for roads.
Your point about places becoming further apart has been made by Cory Doctorow who refers to it as "geometry hates cars".
Edit: found the Cory link - you might find it interesting, but I suspect it's detailing what you already know
https://thewaroncars.org/transcript-episode-79-the-end-of-ub...
Problem? It is THE BEST solution we have. Any suggested alternatives are worse and less convenient.