One reason for the early starts for high schools is that by staggering the start times for high school, middle school, and elementary school, school districts can use fewer buses and fewer drivers. If all the schools started at the same (more reasonable) time, you’d need three times as many buses and drivers and each driver would only get one or two hours a day (and thus would find something else to do, making the existing shortage of drivers even worse). The district I drive for has a transportation budget of about $3 million a year - we would not be able to afford $9 million a year and still afford our administrators’ enormous salaries.

East Asian countries solve this by having the kids take public transit; just run a few extra buses and trains on the routes kids take, then you don’t need dedicated vehicles that sit idle all day.

Not sure which ones you’re talking about, but in Hong Kong, schoolchildren just walk to school. There’s usually a school attached to each housing estate.