How about not having to spend many millions designing, manufacturing and installing large, heavy and complex catapult and arresting gear? How about not needing the extra crew members (including their training, accommodation, food etc.) needed to operate, maintain and repair them? How about not needing to carry bulky spare parts for them? They are a known Achilles heel, because if any element of them becomes unserviceable for any reason, conventional fixed wing air ops are impossible until they’re repaired. And of course the presence/absence of cats/traps is entirely irrelevant to the equally important rotary wing ASW/support helicopter/commando roles.