I have no doubt that this was because I took that time to develop the project.
Keep footnotes and endnotes to a minimum. Depending on the subject and breadth of the topic, some proposals may develop into a full-length monograph c. Take a look at those books and see what their main selling points seem to be. My introduction and conclusion were completely new. Be original. If successful, you will be issued a contract.
If we are going to talk quantitatively, I guess I would say this: if an author wanted to play safe, she might aim to ensure that no more than one-third of her manuscript was previously published.
Again, this is not a problem per se.
It was original. Why should you turn your dissertation into a book, you ask?
But, it was available by the time my book came out. As such, the submission process was significantly easier; the project was accepted, a contract issued, and the completed manuscript took just three months to finish and submit.
Dissertations can run long; books are often far shorter.