I left, married, started a family, and then decided to go back. (I left after having been DF'd) I spent 13 years or so away. I had a personal tragic experience, and felt it was time to get serious about my beliefs. That whole time I never stopped believing. Every time I saw a crazy national, or world event, even a natural disaster, my mind automatically attributed it to the time of the end and the signs showing it was drawing near. I worried not only for myself, but for my family. Perhaps this is his reasoning? 'It might be too late for me, but if I just expose my wife and children, perhaps it will take hold in them and they will become good witnesses as a result.'; this was my line of reasoning.
If he was raised as a JW, no doubt thats a large part in his decision. It can be so ingrained into you that its virtually impossible to forget. If his parents and family went back, or never left, this can play a significant role in his decision as well. It did for me.
In simplified terms, if my parents taught me that the color Orange was actually Purple, instilled it in me, taught me from books, took me to meetings three times a week, where others taught me Orange was actually Purple, told me that my life depended on knowing that as fact. That everyone who ever told me Orange was actually what I was seeing, were all liars and were trying to mislead me. Even after opening my mind to the possibility, and being shown scientific, absolute proof, I would forever have a difficult time ever seeing Orange as Orange. I would always question if it were truly orange, or in fact purple. At some point, it may prove too difficult, even after learning the truth and accepting Orange is Orange, I may make the choice (even subconsciously) that it's easier, less exhausting, less stressful, to just go back to believing what I was taught as a child. After all, it can be easier to not think for oneself, and permit others to do your thinking for you, even if it means giving up the right to choose for ones self. This can happen to anyone, no matter their level of intelligence.