The girls who post about "mental health matters" but they're actually horrible people in real life

Specifically during school years. There's this one girl who particularly annoys me, she never liked me because I'm 'weird', even though I tried to be nice to her for years. I remember seeing that she and her friend bullied a 12 year old who did absolutely nothing to them, she wasn't communicating with them in any way at all. When they were punished for it they were just smiling and said they didn't do anything wrong.

Just recently the original girl I mentioned posted a video saying "always be nice to people" and stuff to that effect. Why are they such horrible people in real life then? Their only hobbies are vaping and sex, and all they like to do is be horrible people.

Edit- I want to mention that I go to the same college as these girls now. They haven't changed, they've gotten worse as far as I can tell, and they're close to being kicked out for bullying.