I was also surprised it hadn’t been the case. Apparently there were some policies against phone use during class but the enforcement was so toothless and sporadic that teachers and kids alike were ignoring the rule.
Now the rules are firm, universally applied, and have actual consequences. That last part seems to be the key. You can try to say phones are banned but until there are actual consequences it’s not really going to make a difference.
The schools in my district did it. Several kids ran huge campaigns with flyers and news media involvement trying to protest it, but after that died down the response has been very positive.
It’s not going to satisfy the people who think that all children everywhere must be banned from social media at all times whether their parents agree or disagree. It does have a very positive impact at schools.