Because while smaller children are physically demanding, there is little guess work involved:
They cry, you can flip through the 3 options of your mental roledex to figure if they are hungry, dirty or tired. And if it's none of those, just chalk it up to that all toddlers are certifiably insane.
Older kids are mentally draining, and there is so much guess work involved, sometimes I get tunnel vision and have all things dissected and under a microscope.* So much in fact, that when I was presented with the easiest question I tripped and had to call a Come To Jesus with everyone in my path.
Belle needed her bedtime renegotiated. But the request came right in between her questioning of why she needed to wear a bra, they were uncomfortable, why I read her texts and didn't let her become an active participant on Maplestory.com** and why I wouldn't buy snowballs. Obviously this sounded more like "I want to be a hippy, circa 1967 in the Haight-Asbury section of San Francisco and score heroin and hallucinogens from strangers!" and "You hate me! And I hate you!" and "Fine, but don't be surprised if I go on a saturated fats binge one day and you have to crack the walls of my house to wheel me out."
After I was able to take myself out of the hysteria the situation presented, I rationalized that my drill sargent-esque bedtime of 8pm might be too early for a 10 year old. But it had nothing to do with reading her baby book and seeing that she has been going to bed at 8 since she was 5. It totally had to do with me picking my battles and not wanting to go to the market that sells snowballs.
*And it has nothing to do with me taking microbiology
**no thanks to twitter!