You are right in one respect - even if the book became a number one bestseller, Peter Thiel is unlikely to feel the impact financially. But since he wrote a book in the first place, he wants something out of it. Whether he did it for money, increased fame, admiration, or respect, the book must do well for any of those things to come.

So while his motivation may be different than most authors, the path he must follow to make the book do well is largely the same. We'll likely see more things you wouldn't expect to see him do. A billionaire's ego is on the line.