Humour me for a moment.
The classic hunter/gatherer model, which humans used as our evolutionary jumping-off point from God knows how far back, is very strictly social.
Think about it. The tribe sleeps communally, generally around a safe point that keeps everyone close together in case of attack by wild animals or roving brigands. During the day the hunters may rove (but often as a pack, if they intend hunt large game) and the gatherers raise the young and tend to whatever non-violent productivity is needed (collecting food or firewood, what-have-you). Of course, without the hunters present, it's probably best to stay in groups and gather together, for safety in numbers.
A proto-human might be born into a tribe of 30 or 40 people, live his entire (40 year) lifespan in the company of those 40 and see every one of them every day, talking to his closest few almost every moment he is awake for much of that time. Sure, there will always be introverts who retreat for solace and quiet, but the lifestyle itself would have necessitated some close connection. Outside of those that he sees daily, he might only see members of other tribes rarely if at all during the year.
Fast forward to the period of cities of a million plus, and a brain that was designed to establish long term relationships with a maximum of perhaps 50 people and interact with them constantly is now regularly exposed to 10,000 people a day, and often only sees a member of that 50 for five minutes out of the day. Perhaps 10 of those people are actual friends, another 40 are passing acquaintances like the bus driver or the corner hotdog stand guy, but the other 9,950 are complete and total strangers. Interacting with them is absurd, as you're likely to see each for only five seconds out of the rest of your life.
Then along comes the internet connected phone, and now, through this magical little window we hold in our hands, we can re-establish the tribal links for which our brains are wired. We can actually keep in constant touch with that handful of 50 or so humans that, five thousand years ago, would have been our 'tribe'.
Then, once you've gotten that relationship nice and established, you take that magical window away for a day. Of course they feel isolated.
Anyway, just a thought.