It's something Google had disabled in Android 4.2 and above. I don't know the reason - something about security but I have yet to figure out exactly what kind of security issue there is.
I am a major customizer of my devices. There are several reasons why I want a main screen switch, but an overriding design goal for me is being able to do things one handed, particularly one thumbed. Fat hands, large phone, means that holding the phone comfortably for me to use my thumbs for most things means that I have to move the phone in my hand or use my other hand to operate the side power switch. Likewise, hard to use two fingers to do something.
I did manage to get the flight mode switch to appear in my notification drop down, so while that is a bit of a thumb stretch it is doable. I am currently trying to find a radio off switch (my old, old HTC had one) which will essentially do the same thing I need to.
As for root, this is a work owned device. And our policy is to not allow users to root the phones. Hard enough supporting them stock! My personal device I would be willing to, but I have so far avoided going to 4.2 anyways and avoided the situation altogether.