>>536820909
>Why is Chaos considered the big bad of 40k again?
It really isn't. It just has a lot of exposure, same deal with Marines. Until recently Chaos was stuck in a small space asshole too. Tyranids are the biggest threat, since they are here it means that they devoured and absorbed at least one galaxy (their own) and so it's essentially another galaxy worth of Nids invading Milky Way. Necrons are right after with reality cheats and science defying understanding. Nobody managed to genocide Orks for 60 000 000 years and they were a constant threat to everyone and forming their empires all the time. Unlike whfb where Chaos is actually some eldritch, primordial threat, In 40k Chaos are just some nascent godlings created by space Elves, godlings which only really came to power not even 10k years ago and only really due to Imperium. Even background weird aliens are a bigger threat, like Enslavers, which actually killed the most powerful species in galaxy and scoured almost entire galaxy of life.