This was posted on one of the videos on the channel of archaeologist Flint Dibble (yes that is his real name, his dad is also an archaeologist and his brother's name is Chip).
As it said, he debated Graham Hancock on Rogan because he felt Rogan's audience needed to hear from an actual archaeologist about the nonsense Graham Hancock was pushing and hopefully get them interested in real archaeology, which I feel is a solid reason for going on Rogan and doing what he did. Too bad more actual experts aren't asked to go on Rogan.
He's hiring a ghost writer because they are very cheap.
When a person dies, they stop needing earthly rewards. And, because a lot of great authors and writers have died, there are a lot of candidate ghost writers, like Martin Amis, Truman Capote and Barbara Cartland. A good spiritualist can summon the right auteur from beyond this mortal coil for any compositional need you have!
That is, if they aren't too busy riding ghost dinosaurs, of course.