Lack of evidence, pure and simple.
Whilst having one of many aha moments a well meaning Christian (non JW) told me God WAS taking care of me and answering my prayers I just wasn't recognising his blessings.
I was trying to escape a cult and realised their viewpoint was just as delusional as the Watchtower and once again I was the one at fault not God. Why couldn't an all powerful omnipotent being just be be a little bit clearer? It was a hard journey but with lots of reading and YouTube videos starting with Richard Dawkins and Derren Brown there was no other conclusion.
The laryngial nerve in the giraffe and Dawkins explaining irreducible complexity of the eye proved there was no God for me.