If you have a budget of $x, do you want to move more or fewer people? Because private auto transportation ("cars") moves the lowest volume.
Further, cars interfere with things that may not have alternatives, like trucks that make deliveries. There tend to all sorts of options for individuals (and the average occupancy of a car is like 1.0) to move hither and thither and yon, but if you want to deliver a refrigerator or a sofa, that's a lot harder to do on public transit—though not unheard of: