pitcher's mound

Watching the girls NCAA softball playoffs made me wonder. Why isn’t there a pitcher’s mound for softball? Or maybe an even better question: Why IS there a pitcher’s mound for hardball?

http://experts.about.com/q/2552/3388045.htm

Baseballs are thrown with an overhand motion (except for those sidearmers and submariners). Softballs are thrown with an underhand motion. The mound gives an advantage to the overhand-throwing pitcher over the batter. A mound would give no such advantage for an underhander.