Publishers get so many books submitted to them that they have to consider the weight of paper and the structural integrity of floors when they lease office space.
They get so many good books that they turn away many high-quality publishable books. When you hear about Watership Down or Harry Potter and the Philosopher’s Stone being turned down umpty-seven times, that is likely to have more to do with the publisher thinking “this is a good book, but we’re already scheduled for the next 2 years and I don’t think we can market this so we can make a profit on it.”
And people write these books completely speculatively, hoping that the editor will like the book enough to publish it.
In such an ecosystem, why do you think the publisher would pay you money for an idea and then turn around and hire a ghostwriter when they can pay an author for a finished book?
(If you were famous and had a name like William Shatner or Tom Clancy that would help to sell books, sure. But you aren’t and you don’t.)
But hey, if you can find a competent author who doesn’t have any ideas, and can work out the details, go for it.