Why working railguns are not yet shipboard weapons

If railguns already work, why are they not deployed on warships?

The demonstrators fire, but the complete weapon has not yet been scaled and integrated into a practical warship system.

The underlying railgun technology exists and test weapons have fired successfully. A demonstrator is not yet a fleet weapon. The complete system must fit aboard ship with workable power, cooling, structure, and maintenance demands. It must also survive repeated use outside laboratory conditions. The engineering challenge is therefore scaling and integrating the gun into a durable combat system, not proving that electromagnetic launch is possible.