"How about urban people who left school at 15 "joined the ranks of the unemployed ... found intermittent work in a number of jobs and also made money as a street singer (Wikipedia)" but became skilled poets and talked to the people who had done those things ?"
There is not a shred of evidence that any of them did this

@Jim Carrol. It's from here: https://en.wikipedia.org/wiki/Ewan_MacColl Now, to be sure, self education would have been a lot harder in, say, the 1700's but there are a whole ruck of people who became succesful in many spheres who did it. Maybe many who, like, MacColl, became involved in the theatre of the time. So why not a broadside writer?