Is it explained why are only Humans so weak to Chaos? And should not Warp and Chaos have access to more than one galaxy? In theory you should be able to travel to other galaxies through warp and warp Gods should be powered by life forms from there as well!? Or did Tyranids already suck everything dry and only Milky Way is left?
I heard some theories, but don't quote me on it.
Tyranids were drawn to this galaxy because of the light emitted by the Astronomican. They also probably ate the whole fucking galaxy where they originated from...
The Chaos Gods are currently limited to influencing only this galaxy. Whether they will influence other galaxies when they grow in strength remains to be seen.
Yeah, Chaos is some scary shit when done by the right author and artists.