Well, the thing with bullying is that it's not always the best decision to fight back. the words you say back to the bully are usually just used against you and create more conflict, so some people just have to sit and take it. being bullied easily strikes fear into other people, so sometimes victims just freeze up and are too afraid to do anything about it.
sources: i've been bullied most of my life and i know how these people work
sources: i've been bullied most of my life and i know how these people work