What makes no sense to me, is that secondary school starts earlier than primary school? Or am I out of touch.
It starts earlier so it can end earlier so that there is time for sports and other extra-curricular activities?
Teachers spend time with students doing these activities, and the teachers have lives too. If high school ends at (e.g.) 2:30 pm, there's 60-90 minutes that stuff can happen and teachers still have 'regular work hours' of 8-4 (a shifted 9-5) so they can do things in their lives.
Activities also can stop during the really dark weeks around the solstice in a way school can't.
Don't necessarily disagree, just laying out a (possible) reason for early start/early finish.