Why navies rarely fitted the largest possible gun

Why did large navies not simply fit the biggest gun they could build?

Because a major power that always used its maximum capability could turn a controlled naval competition into an uncontrolled arms race.

Technical capacity did not by itself determine prudent naval procurement. A small country might build the largest gun it could produce without provoking a general response. A leading navy had to consider how rivals would react to the same decision. Building below the technical maximum could keep a controlled naval competition from becoming an uncontrolled arms race.