The problem is parents and schools must support teachers in screen bans by checking devices into "phone lockers" or a "phone concierge".
A classroom isn't conducive to maintaining order and focus with the presence of addictive distractions.
It feels obvious why phones dominate this environment. If you had a 1:1 teacher/student ratio, nobody would be compelled to distract themselves because the learning is paced for them, not the average of the whole. There's time to catch up on Instagram because roll-call only requires you to answer once. There's time to check Twitter since you finished your test early. The number of places where kids are expected to simply do nothing is absurd - of course they're distracting themselves. I read Treasure Island during my mandatory poetry class, is that a reason to confiscate fiction novels from school premises for their distracting and addicting nature too? The problem is with how we teach.
I'd like to think that mixing enough sugar with the medicine helps it go down for everyone. But I also think it's difficult to make a one-size-fits-all lesson plan for more than 1 person; everyone learns differently, and I don't blame teachers for struggling to discover a teaching methodology that works for everyone. It's a tough problem.
My seven year old get lots of choice time these days in his school. Maybe things are getting better. On the other hand, he finds math too easy, and the only homework he has is what his Saturday Chinese school assigns (daily!).