I think this focus on their being an 'underlying issue' is problematic; many times there is no underlying issue, these are just normal humans with normal brains being totally normally affected by a product that's designed to be addictive. They don't need therapy because there's nothing wrong with them, in fact if there was something wrong with them they'd be less likely to become addicted. They just need to remove themselves from the influence of the addictive substance i.e. put the phone down, socialise normally and build strong bonds with their family and their local community.
People by and large don't need therapy and to pathologise and dwell on nonexistent issues, they really just need to hang out more with other people and realise that what they're seeing online isn't representative of reality.
It sounds to me that we are in agreement on outcome, only that you feel that everyone can get there on their own. In fact you're almost describing CBT without naming it.
I guess my main issue with CBT is seeing it mentioned so many times on reddit, and reddit is such a pathological place that I've come to feel anything mentioned there must be some sort of scam or trick.
People by and large don't need therapy and to pathologise and dwell on nonexistent issues, they really just need to hang out more with other people and realise that what they're seeing online isn't representative of reality.