Also these busses generally go by homes 4x times per day twice for middle school and twice for high school. They don’t go by every home every time if no kid lives on a street, but in suburbs there’s a lot of school bus traffic.
Expanding that to adults would require more trips and a backbone network between collection points. But, the point still stands that sending busses to most homes in America say 40x or more times a day is hardly impossible when we are already sending them 8x a day on the cheap. Being inconvenient compared to a more expensive car option is the core reason why this doesn’t happen.