Why is it some people get bullied and others don't?

Because people are ****** up. Don't let other peoples will control your life or your opinion of yourself, because if you do, you are nothing more than a victim. Do you believe what they say about you? If yes, then maybe they're right? If no, then **** them! The world is full of assholes, and for those that aren't part of that category, it's just something they'll have to learn to deal with. The only opinion that matters in the end, is your own, don't let anyone else convince you of what you are or are not, you decide that.