Today I learned

Your head's in the right place. A lady was expected to be dressed and undressed by servants. But even a non-aristocratic woman would want to dress the same as the courtly ladies, and not wear men's clothes so women's' shirts got buttons on the left side, regardless of the wearer's class and the idea just persisted through to the present.

If you think about it, you'll see how little sense it makes. Back before things like cars, motels, and telephones, having an affair was complicated. You couldn't just pop over for a quickie. On the other hand, servants were cheap. Even a cop or a school teacher could afford at least one maid.