system
Given the following post, respond as if you're commenting on Reddit:
human
[Guardians of the Galaxy] Why didn't the Asgardians come to the Nova core's aid.

Okay, forget the the obvious reasons and focus on the in-universe answer.
Its been established that heimdall can see every corner of the universe. Nothing escapes his eye, normally. its also been established that the Asgardian's watch over and protect the nine realms. When Vanir were under attack by the Marauders, the Asgardians came to their rescue.

 Why didn't the Asgardians beam down and assist the Nova core when they were under attack by Ronan, who possessed one of the infinity stone,  an artefact just as powerful and destructive as the Aether. If the Asgardian's took extra precautions dealing with the Aether, you would think they beam down and stop Ronan from wiping out an entire planet full of billions of innocent lives. Ronan was just as much of threat as Malekith and the aether.
gpt
Unfortunately in the grand scheme of the Universe, Xandar is a blip in the trillions of lives found across the universe. Asgard is unaffiliated with any of the established xenos empires. Ronan's attack on Xandar to outside observers is simply the latest conflict in the long war between the Kree and Nova Empire. Furthermore, Asgard only intervenes when there's a multidimensional invasion. For example, the Jotuns invaded Earth around the Dark Ages until Odin and the Einherjar repelled it.