Why people don't like to talk about Faith

Recently, several people I have encountered have been very hesitant talking with me about their faith.   Some of these people are perfectly comfortable telling me their views on politics, sports, the government, etc.   Yet, when I ask them about what they believe, they instantly close up.

Is this because they are afraid of being judged, or were judged harshly in the past? 

There was one person who said, almost apologetically, that she was an agnostic.   Her whole body sort of cringed up, got smaller as she said this.   My first thought was that someone in her life really cam down hard on her for what she believed.   

Another lady is very outspoken, loves to tell stories and going into long diatribes about her trips, vacations, friend and family.   Yet, when the subject of her beliefs came up, she replied that she was shy, and didn't want to talk about it.

I am asking of everyone.   If I am truly curious about what someone believes, would like to understand them better, and get closer to them as a friend, how do I do this in a way that does not threaten or make them uncomfortable.

I don't care what they believe or not believe.   It actually helps my faith to learn about other people's faith.   Yet, how do I get that across to others?   I am not asking to hurt, to separate, to belittle or to judge.  

Sometimes, people do open up.   When that happens, I feel privileged to hear it.  I feel closer to them. 

So if anyone has some advice, I would love to hear it.