Not defending this necessarily, but people should understand that Australia does food in schools quite differently from places like the US.
We do not have school cafeterias. We have never considered it part of the school’s job to feed children. We don’t provide lunches. We don’t have lunch programs. Some schools do have a canteen where kids can purchase food, but they tend to be run by parent volunteers and they’ve become rarer and rarer as more mothers enter the workforce, and so schools have a lot less parental volunteers.
So in Australia, it’s always been normal for children to bring their lunch to school from home.
And, partly, because of that, it has been normal since the start of generally available education, for schools to set guidelines, and even rules at times, on what foods they consider appropriate and inappropriate for school.
Culturally this is the norm here and has been for a long time - and it’s a largely conservatively based norm.
I’m a little confused because you say the school doesn’t see it as their responsibility to feed the kids but it IS their responsibility to police what they bring from home.
I don’t think EITHER one is the school’s responsibility.