The major alternative would be using a public mass transit system which just happens to hit the school as part of its routes. Which is culturally and ideologically unacceptable for most of the US.

There's some logistical problems to absorbing school busing into public transit. https://humantransit.org/2017/08/the-problem-of-school-trans...

In most suburban and rural parts of the US, there is no existing mass transit system.