I just found a book about abandoned teenagers from the 70s (think juvenile held in post-offense rehabilitation centers) and they speech level is above the average educated adult today.

There's many breadcrumbs like these, of a change in culture globally. 50s social expectations about expression and characters were way deeper. And it gradually fades away as life becomes comfy and entertainment based (80s+) I'd say.

Check out the lead sheet for Stardust, the most popular song around ~1930 https://www.sheetmusicplus.com/en/product/stardust-19425819....

Vs one for Patient Zero, the most popular song today: https://www.sheetmusicplus.com/en/product/patient-zero-24016...