At least 5 years ago, I heard the exact same complaint about what it looked like on your typical college campus.... Dozens of people wandering around the courtyards, faces buried in their phones.
Perhaps it only "seems very abnormal and unhealthy" because we're all part of the older generation that didn't ever have the devices in the first place?
I, too, used to think it was a "disturbing" trend ... but I often find myself doing the same thing now, when I'm grabbing lunch at work or waiting for the metro train, or just waiting someplace in line. Truth is, the younger generation really uses these things as their primarily communications tool. When it looks like they're a bunch of zombies staring into smartphone screens, they're actually *interacting* with each other via those screens -- so it is a form of being social.
And I know in my own case, I was never a very social, outgoing person in the first place. Large social settings full of strangers were always uncomfortable for me. Looking back, I would have LOVED to have a smartphone back then to pull out, instead of just holding a drink and trying to look like I was having a good time.