Milhawk didn't fight shanks because 1) he didn't want to, 2) he didn't feel like fighting, and 3) he was just there to deliver a message. If milhawk was there to defeat shanks, he would have jumped him without hesitation. But since he had no intention of fighting shanks he didn't bother picking a fight that to him had no meaning. I've noticed that about milhawk. He won't pick meaningless fights for no reason, but once he's in a fight, he'll sure as he** win it.
