Why treaty cruisers used four twin turrets instead of three triples

Why did the London-class cruiser use four twin 8-inch turrets rather than three triple turrets?

Keeping within the treaty limit, designers judged four twin turrets more survivable than three triples, even though the triple layout would have added a ninth gun.

The answer treats the layout as a trade between the extra barrel offered by three triple turrets and the resilience gained by spreading eight guns across four mounts. Under the 10,000-ton treaty limit, the designers preferred the latter arrangement. A four-turret ship could retain more of its battery after losing a mount, even though it began with one fewer gun. A proposed late-1930s Royal Navy cruiser with twelve 9.2-inch guns in four triple turrets shows how a larger design could support a much heavier battery.