Why is it ‘sad’? They’re still amused and recording the event, probably to show it to friends later. Maybe they’re not hungry; maybe they’re introverts who enjoy observing and taking things in rather than outwardly reacting; maybe it would be pretty chaotic/messy to have all of them talking with and crowding the woman with the cake in a moving subway… There are many reasons for such a response beside being sad lonely individuals.
