A little more on Broadwell...“Organizations have several tactical reasons to use women,”

[Spike89]

9. Books are time-consuming and difficult

I'm not defending anyone here, but the reality is that even highly educated people can have real trouble writing a book. I'm the acquisitions editor for an ed-tech publishing house and I can assure you that a PhD in no way is qualification for book writing. Even people with advanced English and literature degrees can be pretty bad long-form writers.

Second, if it isn't your first priority, putting out a book just isn't worth the effort for most people. Despite what many think, non-fiction books rarely pay that well. Additionally, many (most) publishers do provide ghost writers for authors. Of course, the author must have a very good story to tell or the publisher won't commit to the expense, but even in my relatively small niche I will provide a ghost-writer/developmental editor to about 5% of my projects. For publishers dealing with high-profile topics, I'm sure the percentage is much higher.

Finally, it isn't at all standard to put the ghost-writer's name on the cover. Some publishers always do, some never, others are situational.