Civillian drydocks are generally larger to hold ships much bigger than a USN CVN, no matter how heavy it is. Merchant vessels of modern age can be three or even four times as heavy as a CVN, without their cargo. Simply look at the largest Cruiseships in the world, all over 100,000 tons, some exceeding 200,000 tons even, much more than a CVN can ever hope to be. Containerships too can be of mindboggling size, not even speaking of bulkcarriers and supertankers. All these ships have to use docks from time to time, requirening facilities everywhere, which is indeed the case.
Beam (width) of:
Largest cruise ship: 47 meters at waterline, 65 meters at widest
Largest Oil Tanker: 69 meters
Largest container ship: 59 meters
Largest Ore carrier: 65 meters
Nimitz class aircraft carrier: 41 meters at waterline, 76.8 meters at widest
So carriers at the deck height are wider than the civilian ships above. If you try to use a narrower pair of hulls and allow the deck to overhang, you will wind up with a smaller volume, and might as well merge the two hulls to reduce travel time to battle stations.