GMorrison
The original design had the then popular 8" cruiser rifles too.
Naval rifles are of "shrunk tube" design, which allows for replacement of worn rifled liners.
Operationally, after expending a magazine of ammo (which was near the rifiling limit of rounds), the ship would return te base and the barrels removed and swapped for new ones. The old ones would go back to the gun foundry to have the shot-out liners removed, and fresh ones installed in their place.
So, you (as a Naval Establisment) wanted three barrels for every one you put to sea. Whic meant you started rifle production early, sometimes before the keels were laid. Once Standarized, you wanted your gun foundries to run at some sort of predictale speed, too.
Which meant you built up an inventory of naval rifles.
Also, doctrine for CVs was in flux, too. Tere was a contemplation that a CV might come under surface assault (say in non-flight conditions, or unavailability of screening ships). And, having 3-4 miles' range on DDs or CLs was seen as a distinct average.
Actual experience taught us that a/c were the much more present risk, and that screening ships were quick and easy to crank out to provect and serve CVs.
That, and no one ever managed to sort out how to make 20cm rifles useful for AAA use. 90 secnds of fligt time is tough to use against a/c at 500 fps. (300kts is 5 miles per minute).