While covering the public domain songs I've noticed in the early 1900s most hit songs revolved around "Mammy" and returning home and about missing old friends and relations that have died. Train songs, murder ballads and drug songs were also popular. In the 1920s it seems it was more about love songs and novelty songs, about popular cities and towns, and about dancing and such.
Today I came across this article talking about how music mortality has changed since 1960, how it's gotten worse - which seems to be evident simply by listening to the music of the last 20 years, so in one sense I agree, but at the same time - it really may be more of a simple re-occuring pattern of songs throughout history. This study focuses only on the 1960 to 2025 period:
From virtue to vice: How the morality of popular music lyrics has changed since the 1960s
https://phys.org/news/2026-06-virtue-vice-morality-popular-music.html
".... The analysis of musical evolution found that song lyrics have become increasingly negative over the past six decades, ... The findings, published in the journal Scientific Reports, suggest that music may act as a powerful cultural barometer, .... researchers discovered a significant shift in the emotional and moral language used in popular music. ... "What we found was a gradual shift away from language associated with virtues such as care and decency, toward themes that reflect conflict, harm and other moral concerns. ... more than 377,000 English-language songs covering 1960 to 2010 were filtered from the WASABI data set and complemented with 5,500 songs that made Billboard's year-end charts between 1960 and 2023. ....
The research found that women artists were more frequently associated with virtues like care and loyalty, while men and mixed-gender groups more frequently reflected negative themes such as harm, subversion and degradation...."