So the obvious doylist answer, is Vetex is just seeing god of the dead and assuming the worst.
However, this is a topic I’ve discussed a lot with others on the forum, and I think there’s an interesting watsonian rason for Hades being an antagonist.
Yes the word choice is intentional, as Hades despite his association with an actual villain Acheron/Durza, is an antagonist.
So the way I see the War of the Gods was a messy brutal affair that left nearly all the Olympians dead. This obviously enrages Hades, who like many of the Olympians didn’t want humanity to have magic in the first place. Now his fears are justified.
So in his anger he gives Durza a curse that could if used correctly gather all magic into a single person that Hades can then trap in the underworld. Not the most thought out plan, but he’s angry and grieving so not exactly in a right state of mind for grand and intricate plans.
So with how poorly thought out this plan is it obviously goes awry. Acheron becomes too powerful for Hades to have any influence over and begins his world conquering ambitions.
Meanwhile Hades hides in the underworld basically just waiting until this whole mess blows over.
It’s in this state that the Peacekeeper finds him. Tired and anguished from what he’s done to the world, his anger at humanity long having burned out. Longing for nothing more than to see his kin again and to see the world healed in some way, he teaches the PK how to destroy curses and let’s PK kill him.