Final answer:
Holden views his brother D.B.'s move to Hollywood to write screenplays as a betrayal of genuine literary talent for the superficiality and phoniness of the movie industry, representing a sell-out for financial gain.
Step-by-step explanation:
Holden Caulfield, the protagonist of J.D. Salinger's novel The Catcher in the Rye, is bitter about D.B.'s work in Hollywood because he considers his brother's writing talent wasted on what he perceives as the phoniness and commercialism of the movie industry.
Holden feels that D.B. was once a terrific writer of short stories, the kind that Holden respects and believes have genuine artistic value. His bitterness stems from the belief that D.B. has sold out his literary talent for the sake of financial success and is now just writing mediocre screenplays.
Holden is bitter about D.B.'s work in Hollywood because he sees it as selling out and compromising one's artistic integrity. To Holden, Hollywood represents the phoniness and superficiality of the entertainment industry.
Holden values authenticity and despises the commercialization of art.
He believes that D.B. used to be a talented writer who wrote for the love of it, but Hollywood has turned him into a sell-out.