The Reason why the World Government went so far as to sink most of the World into the Ocean

I’ve been reading up different theories on why would the World Government went so far as to sink most of the world into the ocean. There were some ideas discussing that way is easier to control to populace, or to sink the Ancient Kingdom technology beyond most people’s reach. But I think the reason might be right on the surface.

Remember, how Vegapunk mentions, that Devil Fruits are born from people’s dreams? Yet he is able to recreate and clone most of the devil fruit powers, so we can assume the Ancient Kingdom scientists could too. How would you fight the army of devil fruit users reliably? What’s the main weakness of Devil Fruits?

Correct, sea water. 20 kings have got their hands on the Ancient Weapon that allowed them to sink the world into the sea, thus quite neatly limiting the threat of different Devil Fruit powers with one fast swoop. Sure, Devil Fruits are always regrow, but in random locations separated by treacherous seas and therefore more difficult to reach than before.