In the 2000s and early 2010s, less of your life was lived on a cell phone or smartphone.
For kids now, it’s 100% of their lives. Post-COVID, the majority of social interaction between peers is through a social media app.
That means that close to 100% of kids are on their phones during the school day. If you aren’t, you run the risk of social isolation and FOMO.
Administrators can’t send a kid to detention for using their phone because ALL kids would be in detention every day.
Here’s one article that examines the problem
Hackers 1995