Because if you don't have some way to deal with Zion, then you're making a build knowing everything you end up doing is just going to get erased by a Golden Fuck You Beam.
But they're all just options. Which means the CYOAs still have to account for people not choosing that option. And yeah, there's more to Worm than Zion. But that's still like setting a dinosaur CYOA a couple of years before the
The problem with inserting into DC, in particular, is that you have a couple of choices.
These are the things that make Worm appealing as a location to use for fanfiction to the vast majority of people:
What I like about it most is none of these things, and if I was to ever write in the setting it would take advantage of them:
Worm powers do not waste time thinking about physics. Theoretically they are based in physics, but, for one prominent example, they are not thinking about the relationship between energy expenditure and effect at all. Perhaps the most obvious case of this is August Prince, as his power relies on simultaneously monitoring the intent of every single person on the planet, yet does only one extremely specific thing to their decision-making processes. It would be easier for his power to just kill everybody who intends to do him harm, but it doesn't, and it won't no matter how hard he wishes or trains it. This is quite distinct from how similar powers are handled in most comic books and superhero stories.
It seems like it in the sense that that's how those cities logically should be portrayed in Marvel/DC, but Worm is distinct in that they actually are treated that way. GURPS Supers was published way back in 1989 and noted that if you think about it, given how a given hero's Rogue's Gallery is almost always outnumbering the equivalent forces on the good guy side, it suggests very bad things for the world in general. Worm, unlike DC or Marvel which are tied to RL's status quo, allows this to actually effect the setting beyond the occasional bit of weirdness. The closest I can really think of is the No Man's Land arc in Batman, but it gets reset button'd in the end just like everything else. In Worm, when the Big Bad Ultimate Apocalypse happens, it destroys the world.
There are horror elements to the setting, but all the references to Entities pre-Arc 26 don't rise far above the presence of mind flayers and aboleths in D&D, and nobody would call a D&D game cosmic horror for their presence.
I think Grumpiest is getting at stuff like Leviathan (introduced at the end of the first arc, Wildbow's numbering be damned), which is effectively Cthulhu: it attacks, you fight it, you lose, then it goes away not because of anything you did but because the stars just weren't yet right (or in this case, because some other unknowable alien god intervened). Behemoth is literally the same thing all over again.
I think what Chastity is getting at is that if there are a lot of villains and they last for a while before getting stopped civilians are going to be in a mindset reminiscent of the Troubles or other long-term civil disorder, which is pretty significantly different from e.g. the IRL 70s USA.
