Commercial ships are not necessarily small. Many are 3 to 4 times the size of the warship in question. When you operate a 260 foot tow/supply vessel with a rig or work barge 1200 feet behind with 100's of lives on it certainly requires attention. A military ship has a much larger crew in order to fight the ship. Something I have never had to do. I have been able to safely operate complex vessels in all weather and traffic conditions for many years with much smaller crews. Much different mind set.
Not only are the commercial vessels much bigger than the Fitzgerald and the McCain, but the bridge is nearly 1000 feet behind the bow, whereas the destroyer bridge is maybe 100 feet behind the bow.