You're absolutely correct. Suburbia is subsidized. sprawling, car-dependent suburbs are almost universally financially insolvent on their own, as they literally don't produce enough tax revenue to cover the colossal cost of infrastructure needed to serve it. They require the financial backing of denser communities to prop themselves up.

The scale of money needed for car-centric development is astounding. Consider Massachusetts:

Using publicly available data, the authors put the annual public tab at $35.7 billion, which amounts to about $14,000 for every household in the state. Those that do own vehicles pony up an additional $12,000 on average in direct costs.

https://news.harvard.edu/gazette/story/2020/01/massachusetts-car-economy-costs-64-billion-study-finds/

Using the numbers from the article, Massachusetts literally spends over 10% of their GDP on cars, more than half of that being public subsidy. Absolute insanity.