I suspect they first became mobile phone friendly. Dumbphones provided kids a way to communicate with parents and the worst distraction would be kids wanting to play snake and/or texting little messages to each other on their T9 keyboards.

But once smartphones came around they replaced those dumbphones and snuck in through the same policies, but in reality they're a completely different category from dumbphones.

Our society isn't equipped to handle new developments like this, and they "just happen" before anyone gives much thought to whether they will lead to bad outcomes down the road.

When an immigrant who was handcuffed and tazed subsequently died in Canada, the investigation started asking questions about the use of tazers. They wanted to see the testing and data that showed they were not lethal or long-term harmful for use on humans.

It turns out no such testing had ever been done. Companies just started making them, so Police forces started buying them and using them on people. To this day there is no data about the consequences of using them.

Same thing for smartphones in schools and a TON of other things in our world.

Getting caught using one (at least with stricter teachers) meant it was taken from you and you got it back at the end of class or even better, your parents picked it up from the principal. YMMV, but that's how it was in Poland in 2005.

Tech evangelists/EdTech salespeople saying that it was the future; there's been a big push in recent years.

yeah I am similarly confused - i went to school in 2016, firmly the smartphone era - and phones would absolutely be confiscated on sight