How does it not apply when Morty is traumatised by the experience? The show doesn't hide the fact that Rick is traumatised (by all of the experiences they had been to) either, he's just better at hiding it.
Your usual sitcom the heroes are infallible and get at most a slip on the wrist. Here the narrator is saying, this anti hero is so bad he could literally destroy the whole world. He can't undo his mistakes because some mistakes are beyond even his abilities to undo.
We're resetting the situation because that's what sitcoms have to do, but it's the opposite of a happy ending. That's the message I got at least. Similar to the vat of acid episode. That actions have consequences and not all mistakes can be corrected.
It's actually the normal sitcom heroes that get away with everything by virtue of plot armor or plot ingenuity, while Rick and Morty cynically reset it because the show must go on, while hinting strongly that this is the only reason it's allowed and consequences were as real as they could be.
Speaking of surprise, your wording implies you haven't seen the show, in which case you shouldn't be reading this thread.
(Spoilers)
In the very first season, there's an episode where Rick reluctantly helps Morty attract his crush with a "love potion". Now this is obviously messed up, but it's a classic trope that pops up in all sorts of mythology. We've all seen it and we know how it goes - generally it blows up in some sort of monkey's paw way and the offenders get some sort of poetic comeuppance, lending the story a satisfying resolution and a clear moral. Rick and Morty goes out of its way to subvert this - it blows up alright, we saw that coming a mile off, but everyone in the world except the protagonists are gruesomely affected. And they don't resolve the problem, they run away. With no negative consequences for them whatsoever. They get to keep living their lives as before, while their original family and everyone else they knew continues to suffer horrifically offscreen. Sitcom does not reset. Morty is traumatized and Rick just shrugs. The end.
This is a shocking thing to see on TV. It sends all kinds of terrible messages. And perhaps that's the very reason why it was so captivating, why Rick and Morty felt so fresh. It was making a very clear statement that in the RIck and Morty universe, normal dramatic tropes don't apply. Poetic justice can't be relied upon, just like in real life. Anything can happen.