Isn't it all an instance of "Ninety percent of everything is crap"? Various people made songs, and various people still do, some for money, some for political purposes, some just for the sake of it. A lot of those songs deservedly die very quickly and a few have lasting appeal.

There is considerable overlap between the ones that appeal to us folkies today and those in the classic corpus from the Victorian and Edwardian collectors, but it's far from perfect overlap. Some songs that were widely collected haven't been picked up in the Revival, and some that are widely sung in the Revival were collected very few times or (breathe it softly) were only written in the 1950s or later.

One reason why a song may appeal to us is that we see it as expressing the feelings of real people in a past age, and that can be true whether it was made by one of the people concerned or by a professional song writer who seems to have understood their plight. But songs can appeal for other reasons. Many ballads appeal simply because they are darn good tales. They can be about ploughboys and milkmaids, or about lords and ladies, or about magicians and witches.