I think the Russel and Rutherford, and many of the early leaders of the Bible Students were authentically seeking answers. When I have read the material, it rings true to me - as in this was what they really believed and there was more explaination of how they arrived at their thinking. I don't think they were snake oil salesmen, I think they were seekers, like the rest of the early religious movements of the day.
As the organization has grown, however, the predictions have failed, and the insiders (GB, Zoner Overseers, Given Ones,) have not displayed the humility to admit where they were wrong or to be transparent about how they arrive at their beliefs. They have had to keep up appearances until they figure it out. They have millions of people hungry for leadership, and someone to tell them they have a right to feel rightous (we are God's Chosen People) and to give them something to blame (Satan, this System of Things, Eve or Sin) for their lives if they don't like how their life is going.
There are a lot of true believers, but how can the leadership tell them, "yeah, sorry - we are wrong. we're not the chosen ones"? They can't. Can you imagine what shape that would leave people in if they admitted that they were just making shit up? The death toll would be high, and I suspect there would be some litigation and jail time. Plus, they have a huge money maker. I can only imagine that once you get in the groove, there is really no easy way to stop it.
All of this makes it even more amazing that people leave when you realize how much they are giving up.