Why modern navies favor single gun mounts

Why have navies dropped dual-purpose twin mounts in favor of single guns?

Because current expected use rarely justifies the extra cost and maintenance, although demanding gun roles could reverse that tradeoff.

The expected use of guns is judged insufficient to justify the maintenance complexity and cost of twin mounts. This rests on assumptions about the kinds of wars the fleet will fight. A single mount looks adequate against an enemy that cannot return fire, especially when the ship can leave to replenish VLS ammunition. A greater demand for gunfire, including air defense, strengthens the case for twins and their higher rate of fire.