There’s something about dancing! Where else than at such a venue would you perform that way; smile at strangers near and far; display exuberance in such an unashamed manner?
Can you imagine the stares that such behaviour would attract in any other situation? The degree of self-consciousness that one would normally feel if one was being watched by a crowd, showing your reactions to your feelings?
And of the music itself: a type of therapy, I believe, that at least for a while makes us focus on something outside our own little world, and can invoke all kinds of emotions.
Music and dancing, especially ad-lib dancing, must surely hold a very special place in society. Where would we be without it?