When a war breaks out, the key is often whether both parties want the conflict. In the event that one of the parties does not really want war or does not want to reach a situation of no return, even if it is superior in strength, be more prepared. You only have one option, avoid bloodshed or delay it as long as possible.
Zeus and Odysseus had already been warned by fast ships from the moment of Penelope's arrest, but even before, in anticipation of what could happen, they had already given orders to all the ships of the Hellenic Navy to fly in stealth mode and not give in to any provocation.
It was not a question of cowardice nor of inability; really, the Hellenic Navy could have devastated the empire's fleet if they had wanted; whoever strikes first strikes twice, and they had the advantage on his side. But that would have thrown the two nations to the point of no return.