The RN carriers and "through deck cruisers" by that time all had the ski jump fitted so there was no room for a steam catapult required to get a Gannet into the air.
Anyway, it wasn't so much a shortage of ASW equipment as they had the necessary helicopters but a shortage of AEWR aircraft which the Gannet had fulfilled. It required the fleet to mount standing patrols of aircraft and picket lines of destroyers and frigates to give warning of incoming aircraft, an extremely costly business.