It is a religious thing and your grandmothers understood it.
"It has to do with the need for regeneration and the strengthening of our spiritual being. God knows that left completely to our own devices without regular reminders of our spiritual needs, many would degenerate into the preoccupation of satisfying earthly desires and appetites. This need for physical, mental, and spiritual regeneration is met in large measure by faithful observance of the Sabbath day." found from a talk about the Sabbath from Elder Faust.
Very few people today even attend church or see it as a commandment.
Am I complete Sabbath day observer. No, I am human and have more work to do in this area.
DJC