Why is that equilibrium impossible for other transportation infrastructure?
In which country? Because they certainly do in the UK - about £10b a year on maintenance vs £33b a year from road taxes. Half that maintenance comes from local property taxation and half from the central exchequer
If you include the societal costs from road accidents it's nearer, with estimates putting all costs from accidents including lost productivity at £35b a year. Throw in global warming and you find drivers only cover about half the costs.
But then people who argue societal costs need to be included never seem to acknowledge the societal benefits of a road network.
The point about social costs is valid, but there's no need to even consider them. The direct costs already need heavy subsidies in many countries.
Fuel taxes raise £25b a year (there's also a "sales tax" on top of that which raises another c. £10b a year)
Car taxes (VED - an annual tax to have your vehicle on the road legally) raise £8b
This revenue goes to the national budget. The national budget spends about £5b a year on maintaining and building major new roads.
Local roads are funded from local property taxes, and the total expenditure on those is under £5b a year.
The government has been trying to wean itself off fuel taxes over the last 20 years -- in 1999 it accounted for 2% of the GDP, it's now down to 1%. As more and more people shift to Electric vehicles the fuel revenue drops. There have been discussions on moving to a per-mile charge, but in any case, drivers subsidise other government funding priorities.
Rail on the other hand is massively subsidised -- on average it's about the same amount of subsidy as the fare revenue. The price charged per mile is far lower for regular long distance commuters (typically those with high wages), occasional use is peanalised. If I go to London at peak time tomorrow, I'll be paying about 90p a mile. If I lived in Brighton and travelled every day I'd pay under 20p/mile. The average rail user pays about 29p/mile (£3.1b and 17b km) and the subsidy is a similar amount.