Jim,
Once again, I repeat, I am not denying or downgrading the people's ability to be creative. The vast majority of the people simply haven't got the motivation or the time to be creative in this way. The vast majority are passive and happy to have specialist people do it for them.

Confession, though I have some of his books, Emrich isn't particularly one of my gurus. Are you sure you aren't misquoting 'ascending' for 'descending'? 'The Lakes of Coolfin' is a particularly lovely song and, though it has been greatly printed on broadsides, versions vary so much and they demonstrate how old it is. In my experience such broadsides are based on real events, and in this particular case I would not like to conjecture whether it first saw light on a broadside or not.

Paul, my argument doesn't fall down at all because we're not talking about how people learn songs, we're talking about how they originate.
And if you're bringing it up to date, which is what you seem to be doing, even more songs nowadays originate under commercial circumstances. And my argument simply says this was, since at least the middle of the 18th century, always the case.