system
Given the following post, respond as if you're commenting on Reddit:
human
[40k] How long until Chaos starts to intervene in regards to the Tyranid invasion of the galaxy?

The Chaos Gods may be dicks but they can't ignore the source of their power/existence being eaten by aliens that don't contribute to the greater warp. It's all good and well for the Imperium to cop the brunt of it but surely there is going to come a point where chaos realises that they are going to have to step in to save themselves. After all during the Horus Heresy (potential spoilers!) one faction had the idea to let chaos win so they would burn themselves out by killing almost everybody, thus the source of their essence. So if tyranids devour the galaxy obviously chaos is fucked. How/when would chaos start to specifically fight tyranids?
gpt
The Chaos Gods won't intervene. They can't. They aren't rational, sapient beings. They have no concept of the 'long game' nor do they have the reasonable faculties required to play it. They are absolute expressions of their emotional concepts, and cannot see beyond them. Khorne is totally incapable of thinking outside the 'martial prowess' box, and even Tzneetch has no long term goals, he simple plots and plans for their own sake (trapping himself as much as his 'enemies').

The Chaos Gods are also inherently self destructive. They feed on emotional response, and to drive those responses they commit violence. The end result of their 'victory' would be the extinction of all life in the galaxy. But then there would be no emotion to feed them, and they would cease to exist. This just reinforces the idea that the Chaos Gods are totally incapable of rationalizing 'The End'.

So... Chaos will never turn its primary focus on the Tyranids, because they are totally incapable of understanding the Swarm as a threat to their own existence.