A book that didn't address the Charles and Camilla relationship during both their marriages wouldn't sell, ('juicy titbits' or not) because (a) Camilla's relationship to the Prince of Wales before, during and after his first marriage is central to the view the British public have of Camilla. Therefore (b) no publisher in Britain would accept a full blown biography of Camilla without that being one of the book's central themes. It would be regarded as of little interest and no publisher, whether small or large, would accept a book for publication that would sell a relatively few copies.
It's not like Charles, where a writer could produce a fairly concise but interesting account in book form of his naval career, or Highgrove and his gardening, or his work with the Prince's Trust and helping to save neglected country houses. However, even POW biographers so far have felt compelled to address the question of his adultery with Camilla and the state of his marriage to Diana, even when they haven't been particularly eager to do so.
In Camilla's book there could be a chapter about Cubitt and other ancestors, a chapter on her country childhood, possibly one on her girlhood and meeting and romance with APB and with Charles, and then....?
99% of readers who bothered to buy the book would be flipping pages saying to themselves 'when do we get to the part where Charles and Camilla get together?' and 'what about the Di/Charles/Camilla triangle,'? etc.
I said in a previous post that we won't get a book on Camilla or one on Charles that has some cooperation from BP and addresses the issues of his first marriage and the full story of his relationship with Camilla, for years, (not one with letters, footnotes, full interviews with those in the know), probably for decades, perhaps not until Charles and Camilla are both dead. I stick to that view, mainly because the two participants alive today and the BRF and TPTB want to draw a veil over that portion of the Prince's life until it is, they hope, almost forgotten.