Two major ones:
1) As has been mentioned, something tangible (homely) for the future - life on a paradise earth (without the extremes of hell/heaven). Many want to see their dead loved ones again, and they only can imagine this in the life they currently live (earth).
2) Probably one of the biggest ones - people coming to YOUR door to show an interest in YOU (feel loved and that the message is vital). Cannot beat that. This one to one contact makes people feel special (no longer lonely), important, and readier to commit to greater cause (the thrill of being part of something grand/urgent). I used to push my beliefs onto the online JW community quite a bit when I first left, and the biggest contention that many of them raised was this: "where are you on a Saturday morning? Not at my door....therefore why should I listen to you?". All these traits distract a person from their issues, bringing comfort/relief.