It follows the lyrics of The Wedding Song by Paul Stookey of Peter, Paul and Mary.
(Second verse)--It was played at our wedding
Well a man shall leave his mother and a woman leave her home
They shall travel on to where the two shall be as one.
As it was in the beginning is now and til the end
Woman draws her life from man and gives it back again.
And there is Love,
there is Love.
My guess is that long ago (look at the Jane Austin era) men were expected to have careers, inheritances, etc. Women were supposed to marry well. It was an unfair system and thankfully women are treated better. I was turned down for a job today by a woman.
I could say that sons are more independent and are less dependent upon their families, particularly their mothers, but that would not be true. I have known a lot of "mama boys" over the years who have neglected their wives because of their mothers. Sounds like an old saying that is really out of date.