In the very early stages of social media, say the era of blogs, MySpace, and forums like these, there were no smartphones.
People would live their normal lives during the day, and perhaps reserve an hour or so of "computer time". Where they physically sit behind a desktop with a keyboard. So for some 90% of the day, they were not distracted by anything, and during computer time, they would find themselves using a device very suitable for deep engagement. On a desktop, it's easy enough to read deep content and to respond at length.
With the arrival of smartphones, social media are with you 100% of the time. It may interfere with your important time (your work, your sleep), but if not that, at the very least it will suck up any spare moment that you used to spent on just being bored or waiting for something.
And as we know, this still is only the basic consequence. It may affect one's relationships, distort their politics, cause depression, and replace healthy physical activities, as the article mentions.
Besides the smartphone intruding on your life non-stop, there's the issue that smartphones really suck. They are poor reading devices and even worse engagement devices.
So content has to be snack-sized. A tweet. A 6 second video. Preferably vertical, to save me from the massive effort of turning my phone. And auto-play, as I don't want to hit next or scroll. This trend of escalating effortless consumption turns into disturbing deficiencies in people. Not being able to focus on anything for any stretch of time.
As an engagement device, it has to be simple too. A like, a heart, and a one-line comment at best, full of typos. Because you can't really type well on a smartphone. So deep engagement is dead, replaced with status (likes, retweets).
This combination of effects (100% with you, snack-size content, poor engagement) can all be attributed to the smartphone specifically, in combination with social media. Not social media in itself.
There was an interesting experiment when I took my niece (18 yo) on a 3 week trip through a tropical nation with basically no connectivity at all. She's the stereotypical ultra addict, glued to her phone all day. Interestingly, not a single sign of withdrawal when offline. She was fine, happy, fully engaged in the real world activities, and not a single complaint.
But then, wherever we would return to a place with a gateway to the online world, all hope was lost again. We don't exist. The country does not exist. Dinner is a distraction. Nothing exists but the phone.
Of course I wondered what was it that she missed, that takes hours to catch up with? Actually, I didn't have to wonder as she explained it by pushing her phone in my face about 30 times per hour.
To show what? A meme. A funny video. Not even good ones, just pure low effort pulp garbage.
My friend is an entrepreneur, running some e-commerce warehouses. He stopped hiring young people. They take 30 minute dumps, 3 times a day. He's made clear policies regarding excessive smartphone usage and still finds them hiding behind shelves on their phones.
It's an epidemic.