It’s a UK thing OP.
In other countries the child can come to school as early as they like and leave when they like (after lessons). The school building is always open up until 9pm or so. It’s a hub for children.
They can do after school clubs, some are free, some are paid for. They can also not do them and simply sit in a classroom doing homework supervised by a teacher, read/ study in the library, use computers to study or browse for fun, use the sports hall/ gym/ pool/ dance studio.
That’s a normal school setup across Scandinavia and Eastern Europe/ Germany.
When I heard school finishes at 3:20pm in the UK and parents pick kids up, I literally went ‘wtf?’
It’s a system that presumes parents don’t have serious jobs. Yes, there are different hours and some have flexibility and home working now, but many jobs (doctor, barrister, police, …) the mum can’t just walk off at 3 to pick up the kids. 10 years ago very few people had flexi hours…
Moving to the UK was also the first time I heard of anyone working part-time or not working at all because of childcare. It had to be explained to me, I just assumed childcare was free or very cheap like in other countries.
These sorts of jobs and lifestyles barely exist in many countries where there are provisions for parents to be parents and have a career as well. Or at least it wasn’t something I ever came across in Europe, I’d never once heard of someone’s mum working part-time, I think there were some SAHMs but not many.