In fairness about "It's a Wonderful Life" not winning an Oscar, the year was 1946 and a truly great film, "The Best Years of Our Lives," won. Hollywood has been incapable of making such extraordinary films for at least the last 25 years, maybe longer.
At the time it would have seemed unthinkable for 'Best Years' not to have won. Culturally it wasn't just a movie. However Citizen Kane lost to John Ford's sentimental swill 'How Green Was My Valley' and in the year of Vertigo...Vincent Minnelli's cavity inducing souffle 'Gigi'.