In fairness, it should be said that this is not just a problem or failing of Jehovah's Witnesses. The New Testament makes it clear that Christians have expected the return of Christ almost from the moment he went away, and that they expected the End in their days...and almost every era since the First Century. They were all disappointed.
Somewhere along the way, Christians decided, perhaps to keep their sanity, to just live the best life they could, and to leave the End in God's hands.
Jehovah's Witnesses have not yet appreciated the wisdom of this. But how long can the boy cry "Wolf!" and no wolf appears, before people just lose interest and stop listening?