During my late teens and early twenties, I was an atheist. I will admit that I was not much like the new atheists. I did not attack people of faith. I was content to just sleep in on Sundays. But I was still an atheist. I am no longer an atheist and there are reasons for that. This is not a list of reasons of why I am a Christian (you can find that here) as I did not move directly from atheism to Christianity. Nor is this an attack on atheism or an attempt to get all atheists to convert. It is simply why I am no longer an atheist.
1. The universe exists.
I had never heard of the cosmological argument but it was basically a version of that. I found that I had trouble believing in the big bang with out someone or something responsible.
2. Life exists.
I still remember reflecting on the nature of life on our planet. Everything from plants to animals to the human body. I tried to imagine how this came about through some mixture in a chemical soup. I found that I did not have enough faith to belief that all this life was an accident.
3. There was no purpose.
I thought I would be happy as an atheist, free from all the religious rules. But the truth is that I was miserable. Life had no purpose. It did not matter if I lived or if I died.
4. There was no hope.
One of the reasons I became an atheist was that I had trouble believing in an afterlife. But as an atheist I realized that there was no ultimate hope. All I had to look forward to was getting old, getting sick and dying. And that was the best case scenario.
5. I believed that there was Someone out there.
I just found that theism took over from atheism. I had a sense that there was Someone out there, Someone watching over me, Someone hearing my confused prayers. I was not ready to believe in the Christian God, but I was open to Someone.
I understand that these things will not push everyone out of atheism. This is only my experience. But it may have something in common with yours.