> amazed to find that the lower classes had
> songs and tunes of their own

It goes back further. If I remember my early/baroque music right, the English upper-class's music (think Henry Purcell et al) died out when it was displaced by music of Italian origin, specifically when Handel came to town. The music composed for one English monarch's coronation* exists only in sparse fragments, and the rest was lost; I've heard some of said fragments, and it's *dire*. No wonder Handel's happy tunes swept the board.

Skip on to the late 19th Century, and we find composers looking for inspiration that wasn't from the Continent. In England, and in the USA, they discovered the lower-classes' music. Cue the first folk revival, and such composed pastiche arrangements as Vaughan Williams's Fantasia on Greensleeves (which embeds Lovely Joan as its middle-eight).

* I forget which one. Enlightenment humbly requested.