I think this more about it coming from a higher authority than the school itself.

Many schools have similar bans but they don’t get support from many of the pupils or their parents as both groups have members that just believe it is the school choosing to overstep their authority.

Now it is a diktat from above it makes the school’s job in enforcing it much easier. They can just point to the relevant legislation/diktat and say that their hands are tied, if you disagree here are the places you can go to voice your opinion. Meanwhile we (as a school) have no choice but to apply the rules, etc.