While these earlier decades of the twentieth century could boast a larger percentage of the population who owned pianos or otherwise played musical instruments, I suspect many collectors of these items kept them mainly for their walls and their scrapbooks.
Sheet music of movie themes continue to be published for modern films, but perhaps used today more in the form of a high school band playing the theme from Star Wars (1979). I don't imagine sheet music from modern films is as popular today among fans who are not musicians.
Do you have any sheet music in your classic film memorabilia collection?