Why reloading vertical launch systems at sea is so difficult

Can modern ships combine the reloadability of trainable launchers with the missile capacity of VLS?

Not without a major redesign that adds handling space, stabilization equipment, and logistics complexity.

A reloadable VLS would require more than placing a crane on a replenishment ship because the receiving combatant must also control and stabilize the load. Sliding or movable cells would consume deck and hull volume, while modular missile barges create their own escort and replenishment chain. Even a large support ship able to shelter an escort internally would add another expensive layer to the fleet train. The alternatives illustrate why navies often accept returning to a protected anchorage despite the operational cost.