I think some people become arrogant when they, for whatever reason, start to view themselves as innately superior to other human beings, and as a result, demonstrate a hostility then they feel that their superiority is threatened. I feel like this really just stems from an insecurity that someone has, like if someone is very intelligent at an elite university and feels that by that virtue they are superior to others and that to them it's absurd that an average person could be better than them.