Why would a bully fake an apology and bully again?

A friend's younger cousin had an issue with a past bully years ago. The bully supposedly apologized and befriended him. But it was a set-up. The following week, the bully said ''We were never your friends, you fell for it'' and proceeded to challenging him for a fight. The bully lost the fight but unfortunately both got suspended for a week. They never spoke to each other since.

What's the idea of bullying, faking an apology and then bullying again? Why do they do that? It did hurt her cousin though. He really thought it was sincere at that moment.

Why would a bully fake an apology and bully again?
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