One question about the Kumbh Mela: I read all about, when, where, who, what... But please explain the Why?

I read all about the Kumbi Mela in the Media. I'm not from India. The stories explain when, where, who, what, the entire history... But please explain the Why? Why is is compelling? Why, as in belief. And Why, as in results or outcomes. Why is this the way forward for Modern India?