Why did women use to wear skirts?

In my opinion, consistent with wikipedia's account, there are two major reasons why women have historically worn dresses and skirt-like garments while men have worn trousers:

Pregnancy: women prefer to wear dresses with no waistline throughout pregnancy, what, of course, men never experience. Perhaps, as past women had many pregnancies, they could never find a time to wear pants! ;)

Religion: a number of religions (e.g. Orthodox Jews, Traditionalist Catholics) prohibit women from wearing trousers and obviously the reason behind such beliefs is generally due to modest laws indicating that women should cover the space between their legs by a garment.

Women started to wear trousers when they actively participated in outdoor works, after the industrial revolution, in the late 19th century. Trousers has become especially fashionable for women since the feminism movement in the middle to late 20th century.