The Government couldn’t find a counter for Kaido’s devil fruit which is why they thought “If we can’t find a counter for it, we’ll just make one of our own.” That’s why they made Vegapunk create the SMILE devil fruit that Momonosuke ate.
Vegapunk thought it was a failure but it wasn’t. Or maybe Vegapunk knew the fruit succeeded and didn’t want the Government to get their hands on it.
How does Shanks factor into all of this?
I think Shanks somehow learned of the World Government’s plan to wage war on the Emperors, and that’s why he attacked the ship carrying the Gomu Gomu no Mi. He wanted to stop the Government from waging war and crushing the pirates.
I mean think about it. What would happen if this war actually took place? 1 out of 2 scenarios would’ve happened:
- The World Government wins and wipes out all 3 Emperors, but be extremely spent after that. They wouldn’t be able to stop the influx of pirates into the New World. And these new pirates would take the place of the 3 Emperors quite like Blackbeard took Whitebeard’s place. And the Government would be too weak to do something about it.
- The Pirates win and the Government is destroyed.
None of those 2 scenarios favor the World Government. I think Shanks convinced them of this. He told them that he’d stand in front of the Throne and guard it and not let anyone else sit on it. Not Whitebeard, not Big Mom, not Kaido. He convinced the Government to cooperate with them to preserve the status quo as. For the next few years at least, their interests are the same. To stop anyone from becoming Pirate King.
The Government did not want anyone to become the Pirate King and Shanks didn’t want anyone other than Luffy become the Pirate King.
Therefore since then, Shanks has been functioning as the Guardian of the World in a sense. Because if he hadn’t intervened, the Emperors or the Government would be gone, the New World would be a place of eternal tug of war and chaos.
*Theory by OkUnderstanding3669