But WHY was Michael rowing that boat?

Possible explanations include Sally winning the arm-wrestling match to see who would row, Sally being only 10 years old and not much good at rowing, but handy with a pair of scissors, (isn't that how you trim sails?) or maybe it was just Michael's turn. The most likely explanation is included in these little known verses of the song. These were collected in the 50's from the clam-boat crews off the Isle of Langerhans:

They're out there on that boat alone
And Michael left his map at home

Mary said we need some course corrections
Why don't you go and ask directions

He refused to do that simple task
Said "Mary, I'll row, if you will ask."

Sorry. In all seriousness, old songs are full of ideas unacceptable today - practically any "ism" you can name. It's a measure of how far we've come that some of the ideas bother us. I wonder what ideas in songs of today will bother us in the future.