Why surface ships prefer standoff anti-submarine attacks

Why did the Royal Navy stop using ship-launched anti-submarine torpedoes?

Type 23 frigates still carry them. Helicopter delivery is preferred for a distant contact because firing a short-range torpedo from the ship means the submarine has already approached dangerously close.

Type 23 frigates retain ship-launched Sting Ray torpedoes. Their limited reach makes them a close-range defensive option, while a helicopter can carry a torpedo out to a distant contact. Firing from the ship can force a nearby submarine to manoeuvre, prevent a first shot, or interrupt a second attack, but it means the submarine is already uncomfortably close. The Type 45 has an air-defence role and normally operates with other fleet assets, so onboard tubes are considered less valuable than the wider force's anti-submarine capability. The preference is to attack the submarine before it reaches a favourable firing position.