I don't get as to why it's so hard to understand this. Some girls, even cis ones, have deep voices. Why is it such a negative thing to not be put into society's definition of what a, "girl", is? And that goes for girls being short too.

Girls who are tall and/or have deep voices are no less of a girl than the girls that aren't. For some reason society favors girls who are short and have light voices. Being bullied for something they can't control is cruel.