Lots of the United States is quite rural, so a bus service would never be able to pick up all of those kids. Only school buses can since the school bus routes are specifically designed to pick the kids up where they are.

as long as the town is designed well.

Unfortunately I have to live in the real world where towns aren't designed well. Besides, the average yard in my neighborhood is 3.5 acres so general purpose public transportation wouldn't work either.

Yeah, in theory sure. We live in reality though

What if, like in much of the country, they don’t live in a city or town?

Except it's too late for that. The cities are already built. Fixing it would require tearing down entire cities and building new ones. Sure, you could do it one chunk of the city at a time, but doing just one city would take decades and exorbitant amounts of money.

A small town is 10,000-50,000 people. Average home price is $300k. There are around 2,000 towns of 10,000-50,000. That's $18,000,000,000,000 to build some of the small towns in the US to be public transportation friendly. Who gets dragged out of their homes to make room for rebuilding?

And you'll still have to problem that many people don't want to live in crowded towns. Most people that like crowded cities are already living there.