A lot of very good answers has been given to this question in this thread.
For me it will be a question about how I feel the day/moment I am given the question and by whom.
Sometimes I would given my reason, other times not.
But I think that when I give my reason, having walked many Caminos, I am focusing on the positive effect it has had on my life and the impact a Camino can have on any life.
To generalise walking a Camino to include people in the past as well as any human now, gives a more interesting answer than my own personal one.
And that may be an important part of my experiences on the Camino - the change of Ego and understanding of myself.
Seeing myself as a part of a stream that have flowed for 1000 years.