I don't understand how nostalgia can be applied to Burning Man.

Outside of those few who dedicate themselves to the organization and administration of the event, each burning man is a unique assemblage of thousands of people, different in every way from one year to the next. Except perhaps the location.

Without the different human beings who show up each year, the event would be nothing more than a dust bowl waiting to become a mud pit.

The "soul," if there is one, is the sum total of the expressions those humans bring with them at any given point in time.

Change the humans and you change the expression. So exactly which "soul" does the author long for?