I asked others on the trek. Many answered “pilgrimage,” and that seemed to explain everything. One traveler who had already walked three times from Le Puy said: “It’s not something I can explain. You must understand it with your heart.”
When I speak to the French, however, I get the feeling that the question is not “Why go?” but rather “Pourquoi pas?” The sheer joy of seeing ancient and natural places, of relaxing among fellow travelers, of walking rain or shine and, yes, of moving toward God seems to be reason enough.
All that said, I can only really speak with certainty about my own reason:
“He makes me lie down in green pastures.
He leads me beside quiet waters.
He restores my soul.”