The authors are required to 'shill' their books. They won't be published if they don't. Writers less well known than Coulter are often times required to go on grueling Book Tours, for up to six months. Hundreds of tiny book stores with 30 or 40 chairs full of book worms asking questions. Hundreds of College Radio interviews.
They are even coached to say 'My Book, MUGGED : Racial Demagoguery From The Seventies To Obama' instead of just 'My Book'. There is no Free Lunch in the book writing business.