It seems that this is an over-simplistic view of the benefits of sleep.
He has a weird sense that you can just sleep whenever told to.
A Correlation Does Not Imply Causation Lie. This is important. since unfortunately correlation and causation are often wrongly interchanged.
To further his career and enhance his reputation and to fulfill his tenure obligations
Not having read the book, I can't know the answer to this
Because he is regarded as the top expert on sleep. this is not acceptable scaring of people.
There are a number of reason for not sleeping, or over sleeping. I haven't read the book, but this seems like an overstatement.
fundamentally. there are many causes for not getting sleep and these may be the actual causes