Most personally convincing reasons you don't believe.

[Aoi Magi]

For me the stories in christianity, islam, and hinduism all seem to make zero sense and often contradict the very god/s they are trying to portray. When I look at the religions I have come across, all seem quite man-made and seem to reflect the ignorance and bigotry of the respective time periods of their origin.

I can't say I lack belief in a god because I am not sure what that term is supposed to mean. But I believe, even if there is a god of some kind, some super sentient originator, at my current level of knowledge I have no hope of comprehending that being until I can reach the same level of intelligence, so I will just keep gaining more knowledge for now.