High schools run early because one of their primary functions is childcare while parents work and parents commonly leave for work between 7-8 so kids need to be on the bus before then. They then stagger primary, middle, and high school so they can use the same bus drivers for all of them and high schoolers leave first so that they can arrive home first without parents. This is being changed as high schoolers need more sleep but it’s not for sports.

In college you need professors to teach classes and most of them want to work a more traditional schedule so want to be there from 7-3