Why wartime acquisitions multiplied Royal Navy gun types

Why did the Royal Navy operate so many different guns in the 13.5- to 14-inch range?

Foreign ships taken over from British yards brought customer-specified weapons that were too costly and disruptive to replace.

British yards built warships to foreign customers' specifications, including weapons that did not match Royal Navy standards. When war caused the Admiralty to take over some of those ships, their existing guns and ammunition arrangements came with them. Changing the armament would often have required rebuilding much of the vessel, so the navy accepted added logistical complexity. The Washington Treaty later attempted to prohibit a belligerent from using warships under construction for another power.