Have come up with some reasons why people bully..remember Jesus asked saul this question, saul saul why do you persecute me? Bullying is basically the same as persecution. Bullies dont let up on their targets.
When Jesus was asking why do you persecute me hes not just asking as if its happening to him personally but anyone who professes his name.
Ignorance - not knowing how another person feels, lack of empathy, self centredness, pride, absence of the holy spirit (who makes us part of the body of Christ...when we hurt, the whole body hurts)
Unbelief..thinking you are lord instead of Jesus. - pharisees, romans...
Jealousy - the other person is righteous or favoured and you are not. Many examples in the bible...king herod, king saul, cain
Hatred...hating ones enemy or seeing everyone else as the enemy - Jesus says to love our enemies and bless those who persecute us.