It's possible that all the Giants periodically just go into a berserker rage and kill everything in sight. This is the "War Land", after all. It's possible they have to periodically satiate their built-up battle-lust.
But, it occurs to me that it could be more than just that. I wonder if maybe Oda could tie this into the cyclical nature of Ragnarok?
Now, in actual Norse mythology, there's some debate on if Ragnarok is actually cyclical and repeating or not. Some sources say there's only ONE Ragnarok with a paradise achieved by the end, while other sources say that Ragnarok repeats itself as part of a natural cycle of death and rebirth of the world, and still others say that the process itself repeats but with different characters with no one getting resurrected.
reddit.com/r/Norse/comments/efl7op/possible_spoilers_is_the_norse_mythos_cyclical/?rdt=55276
https://mythology.stackexchange.com/questions/7837/will-there-only-be-one-ragnarök-or-will-there-be-multiple
https://www.tumblr.com/mostly-history/183340197163/norse-mythology-is-cyclical-and-contains-many
But, in popular culture, this has kind of mutated into the idea that the entire story of the Norse Gods endlessly repeats itself. With new versions of the dead gods being reborn and playing out the same stories time and time again. This is most evident with Marvel Comic's version of Thor. Marvel's Norse Pantheon has died and been reborn multiple times over the centuries, and it's process is overseen by higher-dimensional cosmic entities who use the energies produced by the war for their own purposes.
https://marvel.fandom.com/wiki/Ragnarok_(Event)
So, I wonder if Oda could have the Elbaph Giants undergo something similar to the Marvel Norse Gods? Maybe every so often, the Giants all kill each other or die in some great battle...but then they all also get resurrected again with no real permanent damage done to them. Maybe the power of the World Tree all grants them a resurrection? Imagine it like all the Giants are already in Valhalla, the land of the righteous warrior dead where everyone fights for all eternity. They're all fighting battles all the time, because there is no consequence for killing each other.
Louis Arnote is warning travelers not to stay to long, because this same resurrection magic may not work for anyone but the Giants. Anyone else who's caught up in one of their battles might be killed, and wouldn't be resurrected like the Giants are. Because the Giants might simply not think about something like that while they're in the grip of battle fever. Maybe that's why they keep all the humans locked up in jail cells. It's for their own protection, because they can't come back to life like the Giants can? This could also be why Big Mom is so hated by the Giants. She killed people outside of the time of Ragnarok, meaning that those people she killed couldn't come back to life. It's possible that this magic might only work at certain times. Maybe when flowers on the World Tree blooms, or something?
Could THIS be what Loki actually wants to end? Killing everyone every so often with no consequences? Because I could see someone seeing this as something horrifying that should be put to a end. Perhaps this is even why Loki's eyes are covered, because he doesn't want to witness his friends killing each other time and time again.
Plus, this kind of cycle probably hinders the growth and development of their society as a whole. Elbaph seems to be stuck in the Middle Ages, with wooden huts and more old fashioned equipment. Meanwhile, the rest of the One Piece World seems to be slowly developing into a more modern industrial era. Because there is no incentive for the Giants to develop, as a society. They're big enough that they can just use brute force to solve most problems. And if they come back to life when they die in their homeland, there's no reason to make things better or improve their cities. Endless resurrection could have unnaturally stunted their society's development.
Plus, something like this would tie back into some of the larger ideas and themes of the One Piece story overall. Because there are several hints throughout the story of history repeating itself. This is most evident with Luffy seemingly following the same path that Joyboy once followed, who likely ALSO followed that same path as Nika. The Sea Kings during Fishmen Island mention that "This time will be different". Indicating that there's something causing history to repeat itself, possibly even causing a few characters to be reincarnated over and over again.
Breaking the repeating cycle of history might be the larger idea that Elbaph is all about. Elbaph might be about showing why and how you stop history from endlessly repeating itself. Including possibly ending the seemingly endless cycle of reincarnation. "Staying too long" as a metaphor for "getting stuck in habits" or "letting things play out the same way over and over again". It might be about ending the endless cycle and finding a new path, a new adventure, to follow.
