Most kids that bully others do so because they saw that behavior modeled at home. When you're not shown how to deal with your emotions and insecurities in healthy ways, then they can spill out into rude, bullying, and abusive behavior - particularly if that's the norm for your family. This, of course, doesn't excuse the emotional and physical harm caused by bullying, but it does explain why it happens so often.
Luckily, as bullies grow up, there's often a chance to change course, it's just a matter of whether they'll actually shift their mindset or not. If you're the one who experienced bullying, it's only natural to feel both curious and vengeful about your bully's life course.
A few years ago, I read about a bully I went to school with who was shot and killed in self-defense by a store clerk he was robbing.