[twright0]

The reason that sports dictate school start times isn't difficulty in scheduling practices (since you could, at least on paper, put those practices before school starts rather than after). The problem is that sports are competitive between school districts, so you need shared non-school but school-adjacent time blocks between neighboring districts to schedule games in. Shifting one district much later (to run 9-5, for example) would make it impossible for that school to compete with others after school, which is going to be a practical nonstarter.

In my mind, this is one of the biggest obstacles to changing school timing significantly. Most other objections are internal to a school district, so a single motivated school board could tackle and fix them, but this problem requires coordination between many different school districts all at once.