May Chaos punish everyone!! Cthulhu devoured you, and for that, Chaos will devour him!!!

And the brave fighters of the space marines will destroy the forces of Chaos in the name of the Holy Inquisition and Emperor Sorgal.

and why is it specifically Arandor in the song?).

This is a rhetorical question; the answer is contained within the question itself ;)

The Dimension Door League will not act against this cult because it makes no sense. If God wants to punish a man, he deprives him of his reason, so our intervention here is inappropriate, as someone has already beaten us to it *looks up*.