Before radio and before many people had record players in their homes—and we’re talking a hundred years ago—it was the fashion to have a piano. For many, this was the only way to have music in the home.
Piano owners were the target market of music publishers, the people who commissioned the writing of new songs and then published those songs as sheet music to be used in the home. One way publishers broke new songs was to hire what was called “boomers,” people paid to sing new songs in public, often in front of stores that sold sheet music.
If the boomer and the song were good, people were encouraged to go into the store to buy the sheet music. If enough people did that, then the music publisher could claim that they had a hit song and then pushed it in other cities and on professional singers. More next time.