Again this follows the theory that the Giants don’t actually know a Nika DF exists
There have been very many signs that The Giants don’t know that a Nika fruit exists.
From Dorry and Broggy literally looking at G5 Luffy and saying “Wow, you look like Nika”, instead of “wow, you have Nika df”.
To road and Loki saying “I will become Nika” instead of “I will eat the Nika DF”
To now this scene where Loki obviously knows that Rocks doesn’t have the Nika fruit and yet Rocks’ actions are what leads to Loki thinking Rocks must be Nika.
The Giants don’t know that a Nika fruit exists. They just think “The guy who destroys the world is Nika” or “the guy who saves the world is Nika”. They think Nika is something anyone can become by either saving the world or destroying it. They don’t believe Nika is something you can just eat a df for and then become