Keep in mind that the authors do admit this study to be not much more than a collection of anecdotal statements. While it's certainly interesting, be wary of using these stories to generalize about Christian deconversion.

I'm not really surprised about the reasons they found--while I do not have any serious experience with Christians, I would expect their relationship with God to be treated like any other. What good is a personal relationship if it has to be intrinsically different from any other relationship you have?