I never really thought about it before. Part of me wants to believe it's an effort to inform the person of their possible ban, and another part wants to think there's some kind of 'want' to just call people out and get them banned. Who knows? For 'problem users', the latter is much more likely. Of course, for them, they're banned more quickly anyway.
Either way, reporting is enough. If I ever report a post, I don't reply to the person acknowledging that they've broken a rule. I'd rather just report and be done with it, because that's my 'role' in the situation.