Don't you think there should be more thorough histories of the Witnesses available?
There just isn't a market for it. The only people who are interested in Jehovah's Witnesses are current witnesses, former witnesses, and academics who study religion as a career.
Current witnesses won't read anything not approved by the Watchtower. The former witness market isn't big enough to draw an interest. Ray Franz's book sales were meager when you look at the big picture. It's not like he was able to make a career out of selling books. I've always wondered whether there might be good academic papers (not books, necessarily) that aren't readily available. Stuff like unpublished PhD dissertations or master's theses.
I believe there is a biography on CT Russell, but if I remember correctly it was written by a current Bible Student. It may not be an unbiased source. I've not seen anything on Rutherford. I would love to read a good book on Rutherford.