In the area of content, especially the content of a nonfiction book, several points, not necessarily all, should be emphasized. The publisher expects the author to have verified facts that may be used. Fewer publishing houses today are retaining editors on staff who are charged with catching and correcting factual errors. In addition, the publisher rightfully expects the content of the book to be free of libelous material. It is horribly embarrassing for a publisher, not to mention costly, to discover that a new title is plagiarized from another's work.
Publishers expect authors to bear the responsibility of the editing of their manuscripts.
An analogy might be that of speculative custom house construction. All this is done to insure a more marketable property. The editing and page layout process is simplified by having a prescribed format. There is good reason for this. The process was modernized when machinery was developed where a person keyed in, just like at a typewriter, the text from a typed manuscript.