Man, you guys hate smartphones that much, eh?
They're cool devices, supremely useful, but also a pit of self-absorption for those with ego issues and a giant time-drain for those of us with internet addiction problems.
Personally, I can't stop getting online if I have a smartphone. I find myself fucking with the phone constantly instead of appreciating wherever I am, whatever I'm doing, whoever I'm with. It makes me feel obligated to read every single social media post from my friends, to answer every message right away. It's god damn miserable.
Many other people use them too much to share every single detail of their day or to post a zillion pictures of themselves. Younger generations especially, my own included, have become obsessed with documenting their life over actually experiencing and appreciating it. The ability to get immediate feedback on your posts, your photos, has caused a lot of people to develop issues with self-esteem, or has at least exacerbating existing issues. They can't feel good about themselves unless other people, even strangers, validate them with upvotes and Likes and comments.
On top of all that, what Khem said is quite true: it's hard to keep people's attention when hanging out in person. They keep wondering what's happening on Facebook, how close are they to leveling up in a game, etc. etc. ... so they spend their time on the phone instead of interacting with you. I can't tell you how many dinners I've spent watching someone play with a phone across the table. A lot of folks don't even give a fuck any more if the person they're with doesn't have one and is essentially sitting with them alone and bored. I don't want to go to a party and have every conversation interrupted by someone going, "Oh, hang on a sec." then messing with some stupid phone for like 5 minutes.
Some people are so addicted they can't even stop texting while they drive. Statistics on fatal car accidents caused by phone distraction are disturbing.
tl;dr version: Smartphones are extremely useful if you have the self control to keep them in your fucking pocket when you're talking to a real person or watching a play or driving a car. I do not have that so I use a flip-phone like an old person.