Just speculating here, but my guess is they justify everything to themselves. None who currently run the WT originated it. They all started out as victims too. Just like for many of our family and friends who are still in, it would be painful to see the WT for what it really is.
This is especially true for those who have so much of their lives and identities wrapped up in it. For those at the top, they also have a lot of status, prestige and power. It is human nature to want to keep those things when you have them, providing even more reasons to keep believing.
That having been said, I also have wondered how they could not know they are running a cult. Some of the articles that have been written to defend them against such accusations seem to demonstrate a clear understanding of how cults work. IMO they, like all cults, are able to justify the deception they engage in.
Human beings have an amazing capacity for self-deception. Those who run the WT are no different.