I left because I could see the most elementary of mistakes in counting. Such as 19 followed by 2 not 20. I did all I could to raise such issues only to be consistently met with a refusal to even open the Bible.
Plenty of others I know have left. and what a number of these ones say is that the environment is loveless and cruel. It was the lack of love thy neighbour (a basic Christian principle) that troubled them. Also, lack of integrity, seeing sin practiced but hidden (if you were in the favour with the right people). The current child abuse issues are a good example of this. But wife beating has gone on along with adultery and fraud. Sadly these and other unchristian practices haven't achieved the same level of publicity as child abuse.
Other reasons for leaving is that ordinary people can clearly see that attempts are being made to dumb them down. I have heard it said, "do we really need our brains removing to remain part of this organization?"
An ex-elder explained to me what he had seen happen. He said, say you have a body of Christian men but one turns against Christianity. But he hides it. When the body of elders come to appoint another elder, the anti-Christian one will seek to appoint another anti-Christian one because a Christian would see through him. So gradually over time, the body of elders becomes anti-Christian. And that pattern goes on all the way to the top, so in the end the top is anti-Christian.
Possibly those at the top were always anti-Christian and were seeking to elevate those of a particular persuasion to make it difficult for those at the bottom (who might be believing Christians) and attempt to silence them.