If you reread/watch Jujutsu Kaisen from the very beginning it becomes immediately clear that Gojo was doomed by the narrative from the very beginning.
This man is so powerful he’s the literal Jujutsu society equivalent of a nuke. Power levels are measured in Gojos. Even he tells the elders they aren’t being responsible with the power tiers because there is stuff that goes beyond Special Grade.
The world we are introduced to in JJK is one of entropy. A society that is so relaxed because of the one superpowered man on their side that they ignore the storms on the horizon.
Everything happens because Gojo is too strong, and the powers that be refuse to risk the sanctity of their bloodlines and techniques long enough to create safeguards in case the worst happens.
If it were not for Gojo’s foresight with his students then we wouldn’t have even gotten the bittersweet ending we did. He knew that, as powerful as he was, he was not invincible. He dreamed of the future rather than living in the past.
But the future would never come while he was still alive