Why Brooklyn carried more six-inch guns than the Town class

Did turret size alone explain why the Brooklyn class carried five triple six-inch turrets while the Town class carried fewer?

No; different internal arrangements and the Royal Navy's emphasis on independent operations consumed space that the American design could devote to guns.

Royal Navy cruisers were expected to operate independently for long periods, so they devoted more hull volume to supplies, workshops, and other self-supporting functions. American cruisers could accept somewhat less of that provision and allocate more space to armament. The answer therefore reads the Brooklyn and Town layouts as expressions of different missions rather than a simple question of turret size.