Why sets?
Chris Haigh has an interesting take on why Irish and Scots musicians play medleys/sets of tunes while Old Time
and Bluegrass don’t.
https://youtu.be/ezAA5fkiCdk
I particularly like his conjecture that USA record companies saw more profit in a variety of tunes on one side of a 78 record rather than just one played over and over. An example, for Irish music’s development, of a serendipitous side effect of the lust for money.