Someone in GC responded to someone with "nobody cares" and got a temp. But someone told me to shut up goes unpunished.

Telling someone to shut up is flaming, which is against the rule and arguably worse than "nobody cares".

Why is one punished but not the other?

If you feel like a post violates the rules, you can report it via the report button in the top right of the post.
We do not share information pertaining to action taken against other users, this includes the reasoning behind such actions being taken.
Every report is viewed and handled on a case by case basis.

If you have anymore questions, please feel free to shoot me a PM