But Rocks is intimately aware of the history of the giants
Rocks knows about the secret treasure df of Elbaf. He knows what will happen if Harald eats this secret df. He knows about the Galley Ra, which Harald himself didn’t know about, it was Jarul who told Harald about them, and he knows about w whatever secret power the Galley Ra has
rocks knows all this about the Giants and he somehow doesn’t know about the fucking God of the Giants Nika
The different factions/countries in One Piece each have fragmentary recollection of not only the void century but the general past. When all pieces of information and knowledge are drought to the same place and connected, what do we get? The literal One Piece.
The Elbaf and Ohara libraries are/were early attempts at creating something similar. Both were targeted and destroyed by the world government, Ohara being hit the hardest as even their entire population was wiped out.
The loss of Elbaf's great library stands as an example of what happens when knowledge and science disappear and are lost to the world if its keepers don't have the strength to defend it. Harald believed that the pursuit of scholarly endeavors and a fierce military culture are mutually exclusive and we can all see in what a precarious position it brought Elbaf. The case of Ohara is even more extreme. They were a nation led by researchers, without any significant defensive forces.
The Elbaf library was Ohara's second chance at survival but this time with fierce warriors to protect it. Harald's logical fallacy eventually led to its second death.