on Jane Friedman site:

Nowadays, many writers elect to hire their own publicists. That’s especially true for those who publish with small, independent, or nontraditional presses, since that may be the only way for them to secure media attention. It’s also true, however, for writers who take the traditional route. Unless you’re a major name, your publisher will have limited time and resources to devote to your book. If you want more exposure, you’ll have to make it happen yourself.

Getting a book on the radar of potential readers is a complex, multi-faceted process. An author can do a lot of the networking herself, but it’s rare for her to have the knowledge, contacts, and clout that a professional can offer—and, without which, the radius of her outreach will remain limited. Thus, a partnership with an experienced publicist can be invaluable.