The US subsidizes the hell out of cars, you barely pay for the roads, gas taxes are extremely low among western nations, and annual vehicle fees are, in some states, an inspection, some a registration, etc, but they are rarely more than $50 a year per vehicle.

It also hurts that charging fares the way they do disincentivzes participation. Its harder to do, but as it is the marginal cost of adding people to most lines at most times is near zero given the train is already going to run and be maintained, and thus the added cost burden per added passenger is tiny up to capacity. IE, you want full trains, but not overcrowded trains.

Since the trains will always run, if there is a line that isn't regularly nearing capacity, then fares should be reduced to attract ridership up to that threshold. The problem is that seeing the macroeconomic effect of cheaper transit can take years or decades as areas served by cheaper fares are included to build denser and accommodate the demand for the cheaper transit. But it goes both ways - when the trains feel more expensive, slower, or less reliable than cars, people gradually stop taking the train. When they are cheaper, reliable, and fast people gradually ride the train more, and the city is built around it more. But all these effects take decades to measure.