Well most sororities have very strict hazing policies and many nationals consider an extended pledging or new member period to be a subtle form of hazing. I know we have a national rule that our new member period cannot be longer than 8 weeks and I am pretty sure this is why.
You're definitely not the only one who has noticed this. Many fraternities on my campus have asked why all the sororities initiate so early (early to them because they don't do it until late 1st or early 2nd semester.
But even though our new member period may be shorter, I feel it is just as productive. (Yes our big sisters spoil us, but it is not all about presents)
Anyway, thats my take on the subject.