In his post where he announced he started writing his book, it was clear that he was thinking a publisher would pick it up and give him an advance.
Was he not aware that there were already quite a few books from exJWs, talking about the organization and their own experiences? By the time I'd even heard of Lloyd Evans, I had probably read a half-dozen of them. And did he somehow think there was a large market for exJW material? Crisis of Conscience is easily the best known book about the org, and it's never been a best seller. He certainly knew about that book...
It would fit with the personality of a narcissist, if he thought that his book would be the one to break through and become a big seller. He has made a comment or two about moving on due to the supposed toxicity of the exJW community. Maybe he is thinking that his book on the exJW community will be fast-tracked for a Hollywood script if he only offers to write one.