Why the Royal Navy operated attack helicopters

Why did the Royal Navy have attack helicopters to support amphibious landings?

Because the Royal Marines belong to the Royal Navy, which adapted Lynx airframes to provide the attack-helicopter support its amphibious troops required.

The organizational explanation begins with the Royal Marines being part of the Royal Navy. Amphibious landings therefore create an aviation-support requirement inside the naval service rather than in a separate army formation. The need for attack helicopters was met by adapting maritime Lynx airframes toward an anti-tank standard. Service organization directly shaped aircraft ownership and modification.