Fastening a button left over right (the male way) is supposedly easier for right-handed people than it is for southpaws. The reason for the gender variance is not known for sure, but a widely accepted explanation is that women’s buttons are reversed comes from back in medieval times. In those days, it was common for women to be dressed by their servants, who were typically right-handed.
Another popular (and probably not true) alternative is that men had to keep their right hands tucked into the coats to be ready for swordplay, and that women used the left side of their dresses to protect their babies when breastfeeding