Ron Davies: "But I pity anybody who can't take 4 verses of Hard Times--there are only 4!--or 6 of Lorena. I find both very evocative of a long-dead era when self-created music not pre-programmed for a 90-second attention span was the rule for entertainment."

I agree that some people's attention span is bewilderingly short, and a song that's 6 or 7 min. long, including instrumental breaks and choruses shouldn't really tax one's patience all that much. But I don't think the push for shorter versions always stems from people being borderline ADHD.   In jams, song circles, and singarounds, the reality of the situation may be that one person stretching their turn to 7 minutes results in someone else not getting the chance to lead or present a song. Sometimes the consensus favors going around the circle 3 or 4 times, with shorter songs, instead of once or twice, with epic ballads.   

On the other hand, there's the mysterious phenomenon of the old-timey musicians or the fiddle groups playing the same AA-BB-AA-BB melody over and over for 20 minutes on end.
(OK, it's not really any more mysterious than when the Balkan line dancers link arms and do a Pravo or Les Noto for 20 minutes.   You kind of "zone out" and let the music and motion carry you almost hypnotically, and there's a strong sense of bonding and all that.
I guess what's frustrating is when part of the group is in the mood for that kind of social/musical experience and wants to do 20 min. of "Shallow Brown" in the slowest possible tempo, focusing on vocal harmonies, etc., and the rest of the group is hoping to hear or present a few more songs before calling it a night.)