In the days of Broadsides and Chap Books any well know tune was a good way to carry a lyric - as they couldn't easily print the notation (and would many musicians be able to read whichever notation they chose?). Often there would be a reference to "to the popular tune...." even in Pills to Purge melancholy there are many "to the tune of"'s.

But not all lyrics were worthy or survived. They were the disposable part of a not very disposable culture.