Why modern naval guns usually use single mounts

Why do modern warships generally carry single-gun mounts rather than twin turrets?

Single mounts are usually the cheaper and more maintainable peacetime choice.

A multi-gun mount can concentrate firepower, but it adds machinery, weight, and maintenance burdens. Modern procurement generally favors the simpler mount because navies spend most of their time sustaining ships in peacetime. Wartime urgency might shift that calculation, but it is not the normal acquisition environment. Ammunition-selection machinery would not make a twin mount proportionally twice as large because much of the complexity lies in shared coordination systems.