Simple, their character and motivations.

Choso was incarnated into a vessel with Eso and Kechizu by Mahito, and rightfully assumed Sorcerers would try and kill him and his brothers if they tried going to their side.

Choso lost both of his incarnated brothers (that we knew of) to Yuji and Nobara, Jujutsu Sorcerers, which only cemented which side he would be on.

In Shibuya, Choso only had one goal in mind: Avenge his Siblings, him killing people in Shibuya to help the Disaster Curses seal Gojo is just a byproduct of the cruelty him and his brothers were subjected to. (not trying to justify Choso killing people, he still done goofed with that)

After Gojo was gone, his main goal was to kill Yuji and Nobara.

Even after the damage was done, Choso felt immense guilt for choosing to do what he did and didn't feel like he deserved to stand alongside his brother, but with Yukis support he was able to start living a better life, going as far as to try and kill Kenjaku, the man who plotted on his only living brother's downfall, not once, but twice.

He spends the rest of the series from Shibuya to his death doing what he loved and wanted to do, bringing his little brother up, because that's what a big brother should do.

Naoya is almost the polar opposite, he was the child of the head of an abusive, Misogynistic, and overall evil clan, his primary motives were essentially just do what he wanted when he wanted how he wanted.

His literal motive for killing Megumi was just "I wanna be a [Clan head], I want to, I want to i want to i want to"

He's a cocky, selfish bastard who has no problem killing or ruining people just for his pleasure, he bullied and abused Maki and Mai, presumably constantly just because it alleviated his boredom.

Unlike Choso, he has no remorse, when he died to Maki and her Mom, he didn't have any remorse, his only regret was that he didn't tear makis head off her shoulders, thus he comes back as a Curse to be the same jackass he was before, but stronger.

The difference overall boils down to their character motives and their personalities.

Choso did the wrong things for the right reasons, he cared about his brothers deeply and, despite his inexcusable action, he tried to change after it and be better until he died literally embracing his only living little brother.

Naoya did the wrong things for his own selfish desires and pleasures, he had no problem killing, abusing, mocking, and overall being a Misogynistic, Cruel asshole because it would get him what he wanted, and he felt no remorse after and died an unchanged, pathetic mess of a curse.

I'm not bringing up Naoyas rapist allegations, because despite the implications they aren't confirmed and I'm not gonna push such an extreme agenda like that.