More Americans are profoundly lonely, and the way they work—more digitally linked but less personally connected—is deepening that sense of isolation. Nick Skarda, 29 years old, works two jobs in logistics and office administration in San Diego to keep up with his bills. After a couple of years at the logistics job, he has one friend there. He says hi to co-workers at his office job but doesn’t really know any. “I feel sort of an emptiness or lack of belonging,” he says.  Employers...