The Navy and U.S. shipping industry support the Law of the Sea because it codifies traditional navigational rights such as the right of passage through internationalstraits.
Apparently, by approving our previous signature to a piece of paper, the U.S. will change Iranian behavior by somehow strengthening the American position that LOST's provisions allowing "transit passage" through internationalstraits, such as the Strait of Hormuz, are already customary international law, of which the U.S. is entitled to avail itself.