In his “gritty, well-researched new biography, Mr. Leerhsen tries to explain why a man with legions of adoring fans and the best job in the world would end his life and why, years later, so many people still care about him: ‘authenticity, in the sense of being the real thing and not a pretender, was a lifelong preoccupation’ for Bourdain. The pretense involved in the brand-building may ultimately have been intolerable.”