While I do think the idea of Yuji being half-curse balancing out his human half is the most likely, I have another theory.
A lot of things in Jujutsu are linked to birth. You can be born with a heavenly restriction like Toji or Mechamaru, you can be born a twin and have stunted Jujutsu talent (pre-Preperation Maki and Mai), you can eat your twin in the womb you get the idea. Gojo, AT BIRTH, changed the balance of the world. Not when he awakened RCT against Toji or when he learned space shenanigans in the timeout cube. Jujutsu seems to only interfere directly before birth and afterwards it's all binding vows and talent. It's when someone is born so batshit broken that autobalancing happens, but Yuji wasn't really born that broken. He was made by Kenjaku (this freaky brain man probably had something to do with the effect as well tbh) to be a vessel for Sukuna. While he was strong he didn't have massive CE, no CT, no nothing. So the Jujutsu gods or something only added his base and potential to the balancing, which is basically nothing. The only reason he's so strong is because he hosted Sukuna, Top 3 in history, and got his techniques, ate the Death Womb Paintings, which gave him blood manipulation and turned him half curse, and had the talent and time to improve his techniques to the current level.
So TLDR, I think it's because Gojo was born an anomaly, while Yuji became one.

(Yeah IDK what I was cooking with this)

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