Honestly, I think it is that we are freaks and you guys are normal. :)
Only slightly kidding.
I'm going to set aside the biological element here (which is that couples who are lower in fertility have girls regardless of personality stuff) to talk about JUST personality. Goes without saying that this is much more complex than this because of the fertility/condition angle.
And also please keep in mind that most families do end up with at least one boy and one girl in the mix so it is not really good to overthink any of this since it's pretty clear that everyone can have/raise both boys and girls successfully.
By and large the all girl parents I know are either total disasters (very few and nearly all in real life) or else awesome, great, fully functional women who are very successful and their success is seemingly effortless. I find that far, far, far more girl moms fall into the latter category - like the Sloane category - meaning that you have girls because you make great girls and something in your environment is sending you that signal that girls are a fantastic choice for you (and yes, I am writing an essay on this too, I'm going to get this thread finished if it kills me LOL).
Call it laid back or whatever, girls can thrive in your care, unlike in MY care, where I wonder very much if I'd have driven a girl crazy with my control freak ways had my boys not worn me down first. :) It's not you, it's me, LOL.
So NO, I don't think it is that you can't handle boys, I think it's just that you are so good at girls that some magic happens and you have them. I don't want you to focus on the tiny, tiny percentage of people who ~may~ (MAY, entirely speculative) get girls because they can't handle a wild and crazy, into everything boy because the lion's share of all-girl families get all girls because they do a great job of raising them. That's all. :)

