Why the 1944 Lion design changed its secondary battery

Why did the 1944 Lion-class design replace its 5.25-inch battery with 4.5-inch guns?

Ammunition storage and confidence in 4.5-inch-gun production made the revised battery more practical.

The revised Lion design replaced a smaller number of 5.25-inch weapons with a larger 4.5-inch battery. The answer points first to ammunition storage, because gun count, shell size, and magazine volume had to be balanced inside the hull. It also notes confidence in producing the 4.5-inch system in the required numbers. The change is therefore presented as a fleet-production and internal-layout decision, not simply a judgement about which shell was more powerful.