This idea of bullying rookies might not seem like a big deal when mentioned because, after all, everyone starts as a rookie. And rookies, how could they not get bullied by veterans? As the bullying goes on, time passes, and you become a veteran too. Naturally, you won't miss the chance to bully others, because you were bullied back then. If you don't bully others, wouldn't it be a loss?
This is why, generation after generation, in many scenarios, newcomers are meant to be bullied. If you have to blame, blame the first veteran who bullied a newcomer. Because of him, veterans nowadays love to bully newcomers, and it gradually evolved into a tradition, like in prisons and in European and American Brotherhoods, where such traditions are glorified.