Why don't bullies feel guilty about bullying? Why do they continue?

Because they don't understand the paint and the suffering they put you through whatsoever. They're not you, which might be a good thing.

bullying the part of our childhood and being a part of our life , you cannot stop bullying because it is in our norms.

I guess they still feel guilty in some way. And regret it afterwards. But mostly it's peer pressure and their own discontent. Some bullies are very unhappy with their own way of life and envy people. To make themselves feel better they try to put someone down. It gives them some kind of satisfaction.

Perhaps the bully bullies due to their own insecurities. They bully so that they may feel superior and acknowledged! Not all bullies are inherently evil. Sometimes, they just need someone to talk to, but they aren't capable of simply asking for help.

Sometimes, bullies use their bullying tactics to cope with whatever negative feelings or thoughts they're fighting alone, and just want to take it out on someone else in an unhealthy manner. It's a cycle that keeps continuing if no one (the bully or the one being bullied) reaches out for help.

Some people who bully others don't even know they are doing it. Some might even know exactly what their doing and feel very guilty about it yet continue as it is a way they make themselves feel better about their own self esteem issues.

They bully because they're insecure. They don't feel guilty because they think the person that they're bullying is below them. They reciprocate what they think is right because they don't know what's right. Bullies most likely have been bullied before or put down for the way that they think or act. they don't want to blame themselves so they find someone else to blame. This takes the stress off of them and to them they aren't doing anything wrong. They're just repeating how they're being treated. It's sad but true. This is why we have to be careful bout how we treat other because you don't know if you're creating a bully.