Because it's convenient for the employers of their parents.

It was like this in my high school (France) because they had the kindness to align on the train and bus schedule

Busses. The bus company decides start times in many districts. There are driver shortages and getting all kids K-12 where they need to be on time can be a logistical nightmare.

How strange. In the UK they start at least on 5 o 10 mins. Son's secondary school is 8.30 to 2.45, 3 days there's clubs til 3.45. Primary school was 8.55 to 3.15. I don't think school buses get used for more than one drop off/pick up though (only the late buses return for club pick up)

at a faculty mtg once, a bunch of my colleagues were angry about our bell schedule for the same reason. I asked them why they hated odd numbers so much. They looked at me like I was crazy, although I got that look quite a lot at meetings

Ours is 7:20 to 2:10. It was 7:30, but they moved it back 10 minutes.

Answers to most questions about a school's daily schedule almost always involve two things: transportation and sports. Add in state requirements about minimum contact time and you'll get oddball times.

We are required a certain # of instructional minutes not days. so they make the schedule to where they are in certain classes for a certain amount of time. So on shorter days there’s less passing time. They also have to build in passing time into the day to get from class to class. but if it was five minutes, they wouldn’t have enough instructional time. at my school at least electives are shorter because you need more in the core classes.

Each state/district has specific time requirement to count as a “school day” and “school year.”There’s a certain number of hours/minutes for considered a school day by the state or district. Then passing time between classes is 3-4 minutes. Sometimes bus routes between schools in the district have to be linked. AND, my HS band director always set odd arrival times, like 7:04 because he said it was easier for students to remember.