===It was a marketing strategy for pop music in the last century, collectively launched by the record companies and their DJs===
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Older than that, indeed. Certainly goes back as far as MusicHall/Vaudeville, as in "Marie Lloyd's 'My Old Man'", &c.

On another, just refreshed thread "Songs your mother sang to you", I have just noticed a ref to "Maurice Chevalier's 'Thank Heaven For Little Girls'".

~Michael~