That soon to be end is vital for their enticing appearence imagine what the JWs will think if they tell them that the paradise is centuries away. All sense of urgency will vanish the preaching work of the JWs will be neglected, youngsters will go to uni without scruples, etc. There will be no fear (death at armageddon by not obeying jehovah which means not obeying a manmade org) and of the expectation, if the end is so far off who cares about the paradise. And the org's value goes right down, there is no release in their lifetime from oppression, through its FDS.