Why retain 6-inch guns on the Tiger cruisers?

Why reject completing the Tiger-class cruisers with six twin 3-inch mountings?

Cruisers were expected to retain 6-inch guns, and a battery entirely of 3-inch weapons would have appeared inadequate.

A battery consisting entirely of 3-inch guns would have appeared inadequate for a cruiser. Six twin mountings would provide twelve barrels, but their calibre still fell short of expectations for the role. Retaining 6-inch guns gave the ships the heavier armament considered necessary to make them cruisers.