By this logic: A large portion of roads are low-demand and have few drivers. Why do my taxes subsidize the upkeep of those roads, and not just the major highway

By this logic: A large portion of roads are low-demand and have few drivers. Why do my taxes subsidize the upkeep of those roads, and not just the major highways? Low-demand, niche routes are necessary for a public transit system to work for its users. Sure, 80% of my trips might be on 2 or 3 routes. But without access to the handful of routes I ride the other 20% of the time, the system wouldn’t work for me, and I’d need a car to get around. For example: when I take the bus later than ~9pm, I’m often one of just a few people riding it. But knowing I have the option to take the bus late at night is critical to the system feeling reliable. This allows me to live without a car. Hopefully, this effect reduces congestion in my city, as more people are enabled to live low-car or car-free.