There are lots of reasons, but one might be "Sure there is a God, and he is, or would be, totally angry at me, for all the bad-puppy things I have done." Guilt. Fear.

Getting past that is very hard. "I kissed somebody, and I stole something, and oh dear, I had better shout that stuff down. It cannot be true or I will be whipped by this big meanie in the sky."

Religious engagement is more complicated than that, but we all carry that childlike fear in us.

But it could be a hundred other things with that guy. That just came to mind.

Some people had a bad experience relating to religion, maybe a mean parent, or a mean or molesting religious figure. As religion is very powerful, and can give people power over each other, and that can be abused, and may attract bullying personalities too, that can happen. It is very unfortunate. But it is not God's fault he can't get good help.

A religious leader I once knew, talking about this, said, "The God you don't believe in, I don't believe in, either." That startled people.