kk
The SS38 Exocet was fitted not just to some Leander's but also to Type 21/22 Frigates and County Class Destroyers. So although the RN knew the weapon, the defences were set up for Soviet/WP missiles of the time. The Type 22 Frigates which were anti Exocet capable, were just coming on line as was Sea Wolf which was in it's very early stages of development.
So that's why the high value units had a Type 22 Goal keeper asigned to it, unfortuneately there weren't enough Type 22's to protect all HVU's. Coventry had one with her when she was deployed as a Picket at the North end of Falkland Sound. But, she got between the six attacking A4's and Broadsword, this stopped Sea Wolf from engaging the A4's as it is a "self-defence" weapon.
I'm afraid it was a case of lessons lost again, the Type 42's got Phalanx after 82, but even that was not as good as 30mm Goalkeeper. The 20mm shredded the incoming Exocet but some its of fast moving shrapnel would still reach the Phalanx host. Goalkeeper got its kills further and so the shrapnel falled to travel far enough to reach the host. All lessons that had been learnt during WWII and forgotten.