What dots I am yet unable to connect are those tracing the evolution of the thought processes of a card-carrying, true-believer Jehovah's Witness to those of an atheist.
I think you can lay a lot of this process directly at the door of the Watchtower teaching about God (vengeful Jehovah, in their theology).
One primary factor is that the Jehovah they characterize is so mean-spirited, vengeful, and in fact murdering - a lot of reasonable people would really rather die resisting such a god than voluntarily worship him. Sort of like the locust-creature aliens in "Independence Day" - even if they did have enormous powers, scared everybody to death, and were probably going to kill everybody anyway - most humans would want to stand in line to get into an F-18 and have a go at them.
A secondary factor is that to move on from the JWs and into a mainstraim Christian church, you would have to accept some form of Trinity doctrine in almost all cases. This is one thing that the witnesses were absolutely adamant about - hatred of the idea of the deity of christ.
Third, I have known a number of ex-witnesses that simply lost all faith in any interventionist God long before they left the society. They had been let down by the prophecy, the logical sillyness of the new earth forever, and of course the ugly reality of being shunned over a long fade, that they just quit caring about or depending on a "god concept" at all. So these people quit believing even before they left the JWs.
Then, there are the people who made a careful study of science as part of the escape process. Many science-aware persons see a sort of non-animate perfection in the actual observable universe as it is (without need for a god-personality, like the ancient greeks, romans, or for that matter JWs like to worship). Real science actually does make a lot of the bible seem pretty fanciful, except as creative literature.
For some ex-witnesses, agnosticism or atheism may seem an easier path than finding another flawed church or just going it on your own.