Why do former bullies avoid admitting what they did and apologizing?

If the apology isn't accepted well then that's another story. Their victim has the right to accept or reject but at least it's brave when someone owns up to their wrongs and isn't pretending nothing ever happened like a coward.

I've noticed this in former bullies:

- They greet you after seeing you years later as if you were a best friend they haven't seen in years

- They act like you don't exist at all and even if you post your school picture, they will talk about themselves and how great the field trips were, ignoring you as the owner of the post, bypassing you, not even acknowledging your name... so all of the suddenly it's like you never attended their school; rewriting history

- They claimed not to remember if you asked them about it

Very few actually own up to it and apologize like a mature person. Why is owning up to it and apologizing so hard for people in general?

Why do former bullies avoid admitting what they did and apologizing?
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