The broadside hacks composed re-wrote and republished existing and new songs purely for money. It was their bread and butter. They took songs from each other and sold the street literature through an army of street screamers who were mostly homeless and exploited to the point of starvation.
The folk were not as illiterate as the Edwardian folklorists would have us believe, and kept the song sheets for years. They crop up to this day.
Yes, occasionally the pot poet might push his glass to one side and compose a song of the quality of 'The Dark Eyed Sailor'.
The profit motive what ever it's morality had the beneficial effect of re-enforcing an already existing tradition with the working classes and sometimes the more affluent.
The tunes are a more difficult subject to approach, and a tune may be adapted from the Music Hall the Pleasure Garden, or that which we refer to as art music. Occasionally a completely unique tune might be composed, but very rarely.
Traditional songs do not exist in a vacuum, but this does not devalue them in any way. Sing on!