Yup. To echo the sediment once again; practice, mechanics, and some natural ability.
And by practice we mean PRACTICE. Remember, softball is their job. They can afford to hit the ball 1000+ times a week. That's what they get paid to do. If any one of you got paid to do what they do you would be substantially better as well. That's not to take away from what they do. But for us who have a job that is not related to swinging the stick 1000+ times a week, it's impossible to get that volume of practice in.
And anyways the hitting isn't what impresses me at all. Once you can hit the 15mph 12" yellow ball past the fence, who the hell cares how much farther it goes. What impresses me with some of these guys (mainly the infield) is their fielding ability. Honestly, with the depth of the bases and the velocity of the ball, you have to react quicker than a Major Leaguer. Some of the snags they make are insane. 100% credit to them for being able to do that. That's pretty much unteachable, you either got it or you don't. The outfielders are not so much impressive.