I simply didn't think that there was a single omnipotent entity that controlled everything in the universe. My parents did not raise me to be religious, but they did not raise me as an atheist either. I once went to church when I was young. I thought that Christianity was a valid religion, but perverted over time from human actions. I also believed that other religions like Sikh or Islam were equally valid. As a result, I couldn't adopt any religion as my own. I basically lost any belief in gods because I found that various religious doctrine were not worth holding on to. After seeing common arguments for the existence of God, they did not seem sound and were irrational to me. After that, I completely lost any belief in god or any other omnipotent entity that was controlling the world.
My road to atheism was carved out slowly through education in religion and philosophy. The more I learnt, the less tenable religion was for me. My disbelief in God is simply because I have no good reason to believe in it. ~Darren Wee