The propulsion system has more power than those in the current destroyers/frigates. My guess is that’s needed for a rail gun if that ever materializes. Along with the LCS (little crappy ships) the Zumwalts are examples of ill thought out programs that find sponsors.
Admiral Rickover taught the Navy how to bend Congress to its will. Meanwhile the Star Wars defense concept was made reality by Israel.
Rail Guns seem to have hit a technological dead-end. The Navy specified how many “shots” they required for the life of the rails and the prototypes are far, far below the specification. A half-way realistic fire-mission would wipe out “the barrels” (as it were). Not practical.