The interesting thing about drones is the ability to attack from many directions at the same time, overwhelming the short-range defenses. IIRC no fewer than 5 naval drones attacked the Moskva missile carrier at once, and successfully sank it eventually. Naval drones are compact, barely visible, and, unlike torpedoes, highly maneuverable.
Aerial drones are also highly maneuverable. Large navy ships are pretty tough on the outside, able to withstand a blast of a moderate-size shell or bomb. But they have smaller, harder-to-reach vulnerable areas. This is the kind of target drones are apt to attack precisely.
Most anti-air weapons are pretty expensive to fire, because they were intended against high-value targets like planes or cruise missiles. They are insufficient and wasteful to fire against hundreds of small, inexpensive targets.
It's like having a shotgun and a sledgehammer, but fighting against a swarm of hornets. Despite a large advantage in damage-dealing capacity, you quickly become incapacitated.
