They are hesitant to stand out from the crowd and are reluctant to take action unless others do the same. Observe this man in a blue jacket, who is carrying a laptop bag and has momentarily stopped to assess the unfolding situation.
For a moment, there is a flicker of hope that maybe, just maybe, he will be the one to step up and offer the help that the distressed individual desperately needs. His attention is intensely focused on the person in trouble, and it almost seems like he is on the verge of taking action.