Mens’ buttons are on the right side because men have always tended to dress themselves.
It doesn't mean women do not!!
But years ago (say, during the Victorian Era), the women that could afford fancy clothing with a bunch of buttons would rely on maids to help dress them. So, if a servant is going to routinely buttoning up a shirt/dress for someone else, they prefer to have the buttons on their right side (which would be the left side of the garment).
Wasn't she thought that, she could hire left handed maid...? instead of going against...
Anyway thanks to our beloved kings, though it was difficult for their wives(maids) while buttoning.