Maybe this varies by location but at least in the UK, adults can usually leave the grounds of their place of work during a lunch break. Not true for school kids. And the difference in population density between schools and offices is usually stark.

You can leave your job. You may not be allowed to return to it, but you can walk away.

You can switch your job as desired. Kids can’t switch their school.

You can not have a job (economic consequences aside). You can’t not be in school.

They didn’t choose to be there and if they hate it, the main way out is waiting.