system
Given the following post, respond as if you're commenting on Reddit:
human
[Warhammer 40k/Fantasy] Why do the Daemons of Chaos have such a difficult time conquering the Fantasy world when they have already destroyed countless worlds in the 40k universe?

Daemon technology seems to be identical in both worlds, but why are they more successful in destroying several worlds inhabited by trillions of people with future-technology, and unable to conqueror the fantasy world with probably less than a billion inhabitants with medieval/renaissance technology. And I don't think magic is a constant because both universes draw their abilities from the warp, 40k psykers, fantasy mages.
gpt
They are two very different entities. The forces of the Immaterium in 40k are beings from another, nonphysical, dimension. The creatures of Chaos in the Fantasy are simply influenced by Ancient Dark Magics. 

In short, 40k Chaos is backed by there own fucking universe while the Daemons in the Fantasy are all on there own.