The requests for ghostwriters kind of threw me when I first came to Upwork, as well. I'd see dozens of postings basically saying, Write a love story about vampires for me. My budget is $5. I'm going to put my name on it and sell it to make my first million. (OK, I'm stretching it, but only a LITTLE). If I were to write a decent book that I thought would actually sell, don't you think I'd market it under MY name and reap the rewards rather than take my $5 and let you take the credit and the big bucks?
My idea of a ghostwriter is like what I saw in another job posting. The client said she had a pretty interesting life that would make a great story. She had 20 years worth of personal journals/diaries she had been keeping which she would turn over to a ghostwriter to transform into a book. Another wanted to tell her story in a series of interviews which a ghostwriter would transcribe then rewrite into book form. This is MY understanding of what a ghostwriter is.