Some people try to express their happiness or joy only when there is a chance. They don't want to be one among the crowd. Such people when they got a chance they will express their feelings openly. Other times they will be silent only.
My father is a very good orator. He used to be very attentive during the event or the function. But he used to be very silent. But once he was asked to spell out his opinion he used to make very good observations and people used to appreciate his oratory skills.
That does not leave out the introverts choose to remain a silent spectator in a crowd rather than pulling their socks up and behave like a go getter. The crowd makes them do something because although they have talent , they do not do anything because they are shy in nature. some friends in the assembly know their nature well and initiate the first step. Once the silence is broken, they start enjoying the company of people .