People may talk about it more because it's recent, and the consequences of it (or lack thereof) are more immediate. We saw how that fight with Sasuke and Naruto ended up, and the brutality of their conflict had been set up prior to it. Recall the rooftop scene where Naruto and Sasuke are charging at each other, rasengan and chidori in hand. Their rivalry from that point forward took a turn toward violence, and so when Sasuke actually stabbed him, it was something that had been built up before... and Naruto was not far from that point, either. They didn't end up killing each other, and Naruto was definitely the party holding back--but then, he's Naruto. Sasuke is willing to go that far, because he's the character that has to be 'dark'.
Karin's stab didn't have that set up. It came kind of as a surprise, though the moment she was taken hostage I sort of knew, but it moved Sasuke from killing 'only when necessary' to making against an ally who's only ever been supportive of him. That support of course being in line with the darkness he descends into, but she doesn't need to have the same moral high-ground that Naruto does. Karin is far more passive than she is having a backbone, her agency is completely around Sasuke, and her stabbing and what she resolved afterward was the highlight of her character. Not because I utterly despise her and want her dead, but because for a brief glimmer it seemed that she had learned something even Sakura (whom she's an obvious Part 1 extreme expy of), and even Naruto hadn't--to let Sasuke go. It seemed like we'd start seeing a Karin independent of Sasuke; maybe exploring dialogue with people of Konoha--getting to see what Sasuke CHOSE to leave behind, learning about her fellow Uzumaki, connecting with Sakura.
Or just respectfully slipping out of the manga for awhile, ending on a note of self respect. She didn't though, so for me, the reason why I discuss Karin's stabbing over anyone else is not because of a pain olympics over which was more brutal, which was worse, but rather what it meant for the characters. Karin's handling, agree or not, was atrocious, and we haven't seen ENOUGH build up to buy that such a consequential action like an attempt on her life would garner her forgiveness and devotion with a mere 'sorry'. People mistake Karin's being brash, yelling, and throwing COMEDIC punches around as a backbone in arguments why she somehow works better as a match than Sakura, but this isn't true at all. Karin is incredibly permissive. She cares about him, but she's not really doing anything to help Sasuke off a dark path--by offering her help, and joining the Akatsuki with him, she encourages it.
Naruto's relationship with Sasuke had its build up. Even if the stabbing was equally as horrible, which I dunno it might be, the manga explored their friendship, rivalry, and the complexity of their increasingly turbulent relationship enough that their relationship could 'take that blow' and I can still understand that Naruto wants to stick by him. Karin, in contrast, has nowhere near this amount of development. In her dying moments, she was thinking about the time he saved her from a bear.
To recap: he would have only met her JUST THEN, saved her because I dunno, he was a good guy back then (unless you're telling me 12 year old Sasuke was the kind of boy to fall in love at first sight) and then simply gone back. Then they would have met when he joined Orochimaru, which is a fair two years of development I'll admit, but we never. saw. any. of. it. It's in the land of la dee da speculation and fan imagination. For a man who loves flashbacks, he certainly chose to have Karin fixate on a boring one. So, no build up, hardly the same amount of character relationship, and she gets stabbed.
It's the more problematic of the two, and deserves more discussion because it is just so bad in it's handling. Nobody joked about Naruto nearly being stabbed; or Sakura. Their relationships to Sasuke are usually treated seriously, not that there aren't greivances with Naruto and Sasuke's relationship either. Though by far, of all of the relationships Sasuke has severed by his attempt to murder, Karin's was the one that had the dumbest resolution. In the middle of a war she's getting hot and bothered because Sasuke is around? This is before any 'sorry' mind you (which I see the some aspects of the fandom take as an OK to Sasuke and Karin's relationship).
Bottom line; for me, it's less the act itself, and more what happens later.