I’ve never bought that nonsense about bullies having low self-esteem either. In my experience, they are usually people who were never trained at home to respect others, or (in some cases) they actually had bullying modeled for them by a parent who was a bully. Incidentally, I know someone who says all the guys in his school who were bullies became cops. Intimidating other people gives a thrill to people with a certain personality type.
I dunno - it’s kind of a trait of the middle manager too, if you know what I mean. Saying it’s a sign of low self esteem is like saying rape is not about sex. Sure, it’s about other things too, in fact it’s an extreme form of bullying, but... it’s about sex.