The short answer: because Hollywood declared it so. Of course, that was before 1939 came along and actually became the unofficial greatest year of movies of all time, including the releases of Gone With the Wind, Stagecoach, The Wizard of Oz, Dark Victory, Wuthering Heights, Of Mice and Men, Ninotchka, Mr. Smith Goes to Washington, Love Affair and Goodbye, Mr. Chips. And those were just the Best Picture nominees, excluding The Rules of the Game, The Women and Gunga Din and many more. Well, 1938 did have Bringing Up Baby, Holiday, Jezebel and Best Picture winner You Can’t Take It With You, which I honestly adore. Yeah, there’s something of an imbalance there. The claim that 1938 was the greatest came before the year was through as part of a marketing campaign to get Americans back to the movies. It was still the Great Depression, and by some theories that should’ve meant people sought out more escapist entertainment with whatever spending money they could manage, but the fact was that radio was enough of a distraction and it was free. In spite of a contest gimmick tie-in that I would love to see done today (with or without the cash prize), the plan was a big failure, according to Karina Longworth on the latest episode of her You Must Remember This podcast.