I am guessing that Oracle is worried that if they give up (or somehow lose) the JavaScript trademark, that may threaten their ownership of the Java trademark - the later is far more important to them than the former.
IANAL but seems like intentionally giving up the specific JavaScript trademark would actually help with that, since if a disagreement over JavaScript ever went to court and Oracle lost it could very easily domino into the Java trademark. Give it up and it never goes to court.