This topic has always bothered me quite a bit.
Think of this topic outside of BDSM - vanilla wise.
Just think of the first thing that comes to Y/your head when the word 'brat' is mentioned. i guarantee Y/you it's not associate with something positive. Even the way the word is pronounced is....crude (mightn't be the right word to use). Typically, i don't know anyone who uses the word 'brat' and finishes the sentence on a positive note.
i don't know about how others feel, but when i was in primary/high school, i just wanted to smack the crap out of brats and make them shut up because all they did was complain and make life miserable for others. i don't and can't associate that with powerful and commanding like Y/you can with the term 'Dominant'.
Dominant's have a certain force and power over subs that it makes the sub voluntarily bow down. i mean think of it in a top down organisation structure. Y/you don't get to the top by being whiny and bratty...Y/you get to the top by being Dominant.
If you're a sub and you bow down to a brat voluntarily then you've got to grow up.