Because many people have first hand experience that the Source of reality is interacting within their life, with tangible things.

Then they seek what caused it from books, were some of it is ancient superstitions; yet some is based on the same Source of reality, inspiring some people within their life.

To dismiss all of the evidence, without a careful investigation is foolhardy, as if we exist within the Source of reality (God), and ultimately we have to honour that concept to exist; we do ourself in by rejecting it.

It would be like saying there is no CPU, when we're fictional computer game characters, as we've never seen the processor that makes our reality.