Another quote from Roud's book, here quoting Charlotte Burne in the last part of the 19th century;

"One such song-maker, commonly called 'the Muxton carter' ... ... used to think the verses over in his mind when he was going with the horses... ... It was doubtless such unlettered poets as these wh supplied the matter for the broadsides which emanated in great numbers from Waidson's press at Shrewsbury during the earlier years of the present century"

So far in the book I haven't come across what I would recognise as a 'broadside hack' as referred to in this discussion. This is reference to many sorts of people, with varying degrees of education, who's work came out on broadsides. To me the simple interpretation is that they area a result of straightforward business decisions on the part of the person with the words, the person with the press and the person who sold them. The arrangment may or may not have been equitable amongst the parties concerned but they all must have thought that it would help them keep food on the table.