If Ragnir was a devil fruit weapon, do we think it was on joyboys crew too? Zunesha was important in Wano, and Emeth in Elbaf, so maybe it too is a remnant of the dreams of the past. We don't know if lifting ragnir is a matter of pure strength (scale wise its massive, reminds me of playing armored core and seeing just how tiny the doors are) or some sort of a "worthiness" thing like in marvel. I bet its that the soul within the weapon still has an old dream it wants to see fulfilled like Emeth and Zunesha.
Or as theorized by some a really buff squirrel was guarding it and threw the hammer