It isn't usually necessary to ride the lift down, because most resorts provide an on-slope escape route. There's usually a catwalk, even on the steepest slopes. But somehow people manage to miss them. People like my seatmate. And he's not alone.
Folks also manage to miss trail markers designating the difficulty of the slope.
Some resorts have installed gates to force people to stop, read the warnings and consider the choice they're making. Apparently sometimes even that doesn't get the message across. I've skied a couple of runs where the top is marked with a skull and crossbones. But no amount of signage can prevent skiers and snowboarders from getting in over their heads. Perhaps they're distracted by the scenery and not paying attention to where they're going.