Shame is usually deployed when someone “should already know better” and usually does not accompany an explanation, unless the shamer is feeling instructive.

Used to go to communities online that mocked others’ behavior. Sometimes, the “wow what a worthless human being, the world would be better off if they weren’t here” comments also add “couldn’t be bothered to [do good thing X], what a [bad trait Y]” or “what kind of monster does [bad thing X], how [bad trait Y] of them.” Socially inept teenage me found this very instructive on what was acceptable and what was not, especially since I was inadvertently provided the why. (I avoid these types of communities now as a hopefully more-well-adjusted adult.) People can absolutely use their words to explain why something is shameful… at least when they are pretty sure everyone else is on their side, and the person being shamed won’t be able to retaliate (I am sure whoever is filmed for r/noahgettheboat isn’t aware they were posted on Reddit) or will be downvoted a lot if they try to defend themselves, whether justifiably or not (people judged assholes on r/AmITheAsshole).