Rather broad question, but here goes:
Krakauer's interest in the story likely grew out of his own desire to challenge cultural norms, particularly when it came to taking on challenges of the great outdoors. He saw McCandless' story as a sort of epic struggle between the society and Chris' desire to live outside of the regular rules in a way.
Chris in some ways grew up with such huge advantages, a nice home, a nice school, admission to a top college like Emory and has all the opportunities that come along with it. But he still fought against it, eventually had to disappear and not be in contact with his family anymore, etc.
But those two forces are still obviously around and the story obviously draws a great deal of its power from the conflict between them.