Here are my thoughts....for the really young girls, the one who can catch goes to first, the one who can throw far foes to 3rd, the really bad ones go to the outfield, the one who fits into the gear catches, and the others go to middle infield. As they get older, the better of the middle infielders move to shortstop because it's perceived as more important. That leaves 2nd base empty. Think about it...who really wants to play 2nd? It's extremely important but it's not as 'cool' as the other positions and gets close to no recognition, so nobody really wants to work at it to become great at it.
That's just what I think...and I agree that most 2nd basemen are not up to par with the rest of the infield..