As many people are spreading misinformation here:
This game is not "banned" in Germany. Valve is not a branch of the German government yet. Therefore their decisions are not legally binding in this way.
The Fear and Hunger games are not even on the index that means there isn't even an advertising ban. And even the "confiscated" state in most cases does not mean that private ownership is illegal.
This is a Steam issue not a German legal issue.