One aspect of "decline" is not so much in numbers, but in the presence in their midst of the 100% J.W believer, who goes along with all the nonsense.
All the J.W's I have spoken to in the last couple of years expressed their doubts about it being 100% "the truth. When I was in the number of people who I would rate as full believers* was well over 90%. Most are now in just for family and friends, not belief.
* By full believer I don't mean the out and out fanatic J.W, there were some of them, but those who supported nearly all of it, if having underlying doubts perhaps.