>>149236163 (OP)I have no idea what happened to whoever you're talking about but- Fear.
They see people getting cancelled for similar shit constantly. It starts to feel less like "will it happen to me" and more like "when will it happen"
By bringing it up themselves they hope it'll soften the blow. That people will be more willing to forgive them if they say how sorry they are without having to be called out first. They believe it gives them more control over the narrative.
It obviously doesn't work though. It doesn't matter what it is you did or how old you were when you did it. It doesn't matter if you've changed a lot and regret your past. If you have a large enough following people will want to see you fall and will take every opportunity to do so.