...because it won't cost them anything and there won't be any pushback because the vast majority of schools banned phones years ago.
Perhaps they could also ban kids running in corridors or pushing in the lunch queue.
What a waste of time government this is.
(by 'banning phones' it's generally accepted to mean kids can have them in their bags but they must be turned off or at least on silent and never seen - so any parental cries of 'but they need them for the journey home' are irrelevant.)