Since the person promoting the book has literally no interest in the content, it doesn't make sense that the writer would be an expert, nor that the book would be any good.
An expert ghostwriter would be undercut by a ghostwriter supplying copy-pasted material just good enough to get past the publisher. A publisher who actually cares about whether or not the book is worthless would outbid this publisher for the skills of the expert.
The problem is that if you're looking for information about a niche subject, there are sometimes independent researchers who study for their own fulfillment, and then self-publish or publish through small publishers or vanity publishers. If you happen to find a book like this it can be a treasure since it's literally several years labor of love on the topic you want to know about. That person is also happy to have reached someone interested in their topic, even if their financial reward is negligible, zero or negative.
Because of the 'business' described above, that book is now impossible to find. It's been swamped by hundreds of easily generated titles which are at best copy pasted from the wikipedia, at worst utter gibberish.
An expert ghostwriter would be undercut by a ghostwriter supplying copy-pasted material just good enough to get past the publisher. A publisher who actually cares about whether or not the book is worthless would outbid this publisher for the skills of the expert.