People in the country already pay more tax because of the distances involved - they use fuel to travel and the fuel comes with fuel excise.
I’d speculate that the feds don’t want to give up fuel excise because it is such a money spinner for them and it is not easy to cheat on. The money goes into general revenue, the roads stuff is just a red herring.
To impose a federal mileage tax, would *I think*, need agreement from all the states (remembering back to the introduction of the GST).
At the moment the states look like structuring it as a fee within their own remit. So they are going to be able to extract tax for themselves that the feds can’t touch (think redistribution of GST). For the populous states this will be a really significant amount of income.
If the states agreed to a federal mileage tax then they would be giving all that away. So I can’t see that happening, despite the clear advantages in terms of uniformity and justice.
The feds are certainly watching on in horror and will be thinking of ways to change the way the federal taxes are distributed back to the states.