Sit-down toilets are a relatively recent invention. In many parts of the world, they're still basically a hole in the floor, maybe with somewhere "official" to put one's feet, and squatting is the norm for women and for anyone doing #2. Standing is far more comfortable than squatting, so why wouldn't a person stand to pee if they were equipped to do so?
Bonus factoid: In Victorian and earlier times, European and American women wore no underwear beneath all those skirts and petticoats. They could, and did, "go" anywhere (outdoors) easily, and in complete modesty.