But it goes beyond just subsidizing roads and fuel and SUVs. The federal and state governments subsidize rural and suburban power networks, water distribution, waste disposal, schools, police, firefighters, doctors, telecommunications... a whole host of things that drive down living costs in rural and suburban areas.
Yes, it's cheap to live outside of cities (in the US). Nobody's debating that. Nobody's saying it's not an appealing lifestyle for lots of people. We're saying that the reason it's cheap is because it's subsidized. It's basic economics. There are precious few places in the world where "it's just cheaper to live outside of cities" without strenuous government intervention.
Power generation, water distribution, waste disposal and the like are typically done outside of urban centers because the denizens would cry NIMBY about the effects.
Those supply networks exist to service the urban centers, it would be wasteful to not use them for the suburbs that they necessarily have to pass.
Additionally, cities pull in food, power, water and other things from rural and suburban areas that exist to support cities.
I do not support commuter culture, but this is a far more complicated issue that car subsidies. There's a huge interconnected web of incentives at play. Any disassembly needs to be done carefully.
That's part of it. But it's also just cheaper to live outside of cities. If you live in a place where land is plentiful, you can have a big house, a garage and a big box store a few miles away. You can get to places on interstate highways (which are not going away because of their economic necessity). This is, for many people, an appealing way to live and a way that requires a car. Where I live it wasn't until mandatory parking in the city that people started to drift back downtown to live.