The other way 'round, sah. Most of the people I know who became atheists were faithful enough in youth. It was usually in their teen years that they started drifting away, not because of any new information or a real change in belief, but because they simply got distracted. Life was happening, and they wanted in on it. If they were of an intellectual bent, they never bothered to study Christianity.
Eventually… they forget, and then imagine they were outgrowing something childish. I suppose, in a way, they did. They outgrew their young Christianity. Most never stopped to ask if there might be an adult Christianity.
But in direct response to you, I would also point out that every discipine is frankly complicated, highly arcane, and usually far-fetched on ths surface to those who don’t investigate it, Physics, chemistry, economics, psychology, literature - I find any of those more difficult to grasp than Theology.