Why Lexington and Saratoga carried eight-inch guns

Why were Lexington and Saratoga so difficult to bring within treaty displacement, and why did they retain eight-inch guns?

Their battlecruiser-conversion compromises created weight problems, while the heavy guns made sense for fast reconnaissance carriers expected to operate with or ahead of the fleet.

The eight-inch battery reflected an early expectation that these fast carriers might scout ahead of the battle fleet and meet enemy cruisers independently. Aircraft were not yet treated as a decisive anti-ship weapon, and the United States had relatively few cruisers available for screening. The armament looks excessive in hindsight, although it fit contemporary uncertainty about carrier employment. The discussion also distinguishes the Lexington class's battlecruiser-conversion weight and balance problems from the doctrinal reason for retaining heavy guns.