There's more to this world than cities and suburbs. Ever visited actual countryside? Most of the the larger roads out there are necessary to deliver food and other goods to cities. When they have to exist anyway, it would seem incredibly stupid to tax private car ownership outside of cities more than necessary.
A lot of those roads could be train tracks instead, FWIW. "Most of the larger roads are necessary to deliver food to cities?" Not at all. The smaller roads leading to a hub? Absolutely. But roads have terrible throughput.
And as others have mentioned, just because something is necessary, doesn't mean we should subsidise it. Especially when rail and (contextually) river shipping exist and are often cheaper.
