It could be that they think in the tangible sense that anything that exists must be able to be proven. Many highly intellectual people need proof and evidence of something to ever believe in its being. Some philosophers and sociologists are not this way as they create a thought and see how society relates to it or use philosophy to explain something. Religion in some ways, is a philosophy.
Religion could be seen as a way to keep going in life. To have faith in something that is unseen often gives people a meaning to their point of being. People use religion to talk to a God or to ask for help from angels in hopes that there is something out there to help them through. One would think that a life without some sort of spirituality or religion would be a life that has no meaning.
For many, having a God or something to believe in is as essential as breathing. Varying religions contradict each other so much. Hundreds of religious views are followed by a group of people. Is religion a form of brainwashing? Religion and a belief in a higher power could just vary so much because for each person, that is what works for them and it is what they have come to know.
Not that all people who believe in religious views are naïve. Those who are atheists, certainly are not naïve into believing that there is some other power that is accountable for all that is incorporated into being. They are not willing to turn their lives into something that they cannot see, hear, feel or touch. To have faith in a god is to believe in something that cannot be felt among any of those senses but to only read teachings of those that came before us.
There is controversy about the actual term atheism. The word is of Greek origin of a combination of “a” and “theos.” The true meaning of “atheos,” though is questionable.