I have spent considerable time researching the question “why softball instead of baseball?” The only real answer I found was simply, tradition. Why do 7-12 year old girls play softball? Because that’s what they’ll play in high school. Why do they play softball in high school? Because the college’s play softball, and if you want a scholarship you won’t get one for baseball. Why do they play softball in college? Because all of the girls coming out of high school play softball.
I believe Phish Head’s assumptions about girls/womens softball are almost all wrong. I think perhaps he’s confusing their game with men’s beer league slow pitch softball. Girls can and do through the ball very fast, and at the youth level, it’s my observation that they are usually throwing faster than boys of the same age. ESPN televises a lot of college softball (though the season is over now), and if you watch just a little, you’ll see that they throw just as many breaking balls and off speed pitches as their male counterparts in baseball.
When softball originally emerged as an altenative version of baseball for girls, some minor rule changes were adopted to make the game easier. Almost all of those rules have been dropped or adapted, save for the use of a fourth outfielder and the absence of a pitching mound (which is impractical for underhanded pitchers).
Softball was originally played with a ball that was larger and softer. Now, it’s just as hard as a baseball, and only slightly bigger. Girls and women use an 11 inch ball, while a baseball is typically 9 inches in diameter. Because it is bigger, a softball is easier for beginners to learn to hit. It also makes it harder to throw, particularly for pre-teen girls with small hands.