They claim to love Jehovah unconditionally but saving ones own hide is the major motivation especially since JW men are made to feel as if they'd be jeopardizing their eternal life if they didn't reach out for position, although being able. As a side benefit, they enjoy the accolades of their peer group and often times they make their wife proud of the feather she gets to wear in her cap.
Same goes for the door to door ministry. JW's claim obedience to God and love of neighbor is the main motivation but if they weren't so thoroughly convinced that eternal life vs eternal punishment was just ahead, it is highly likely that wouldn't do any of it. The higher ones level of service, the more likely it is that they'll get an eternal reward and enjoy the accolades of their peer group.