Over a decade ago, I was approached and asked to co-author a book. It was a technical book that related to my job. There were 5 of us involved. The publisher rejected the 1st draft. The reason, "It is not thick enough". The publisher wanted a book that was at least 2" thick. This was so it would "stand out" on retailer's shelves. We complied by adding a lot of fluff. For one reason or another, a fight ensued between the lead author and the publisher. The book got shopped around. Another publisher picked it up. It lasted 1 month on the shelves. During all the haggling and bickering, the field had changed resulting in a book with dated technical information. My total profits amounted to less that $1.00 per hour.
That was the end of my book fantasies. I admire anyone who undertakes it today.
Pete