Because that is a non-standard word, we do not accept it. I could maybe see a situation where we could accept it for "Teyze" (used when referring to any older women), but in general, we stick to Standard American English while accepting British English alternatives :)
Really? I didnt realise Auntie wasn't a standard word. We do use it in British English, perhaps as an informal word for aunt. Is that what you mean when you say its not standard?