As a grown up, I've considered giving up my own smart phone but friends use whatsapp/viber, traffic in the city is getting worse every year and an app like Waze becomes essential, depending on what you do, reading and replying to email while on the go can be pretty important.
Similarly, growing up in a society where your peers connect pretty much exclusively via social media, you simply need it if you want to even remotely fit in (like others have pointed out).
Not having a smart phone is not the end of the world (for me or the teenagers in question) but there will be daily negative consequences.
The problem is not the tech itself but the way it's being used. It's the whole reason I don't really like having a smart phone (while also enjoying many of its features).
I want a utilitarian tool that gets done what I need done.
If I use a socket wrench to remove a bolt, I expect the wrench to just do it. I don't want it telling me about some fancier wrench available or a better bolt to use in the future or anything else I didn't ask of it.
What I get instead is a platform where I can be targetted, sometimes obviously, sometimes invisibly, as a potential customer of some business.
On top of all that, you know the device is easily damaged and doesn't last very long because of a quickly degrading battery. And good luck finding a good quality battery after 2 years or even easily replacing it.
Screws are the biggest faux pas you can now commit as a manufacturer. You'd probably sell more units if some of them spontaneously combust than if they aren't all smooth and glossy.
Any attempt to make a human-centric smart phone (and underlying OS) is doomed to failure because of cost.
But hey, current smartphones is what people want so what do I know.
Anyway. Did I mention I don't like smart phones?