Why don't aircraft carriers have multiple sets of arresting wires?
Having a second set of 3-4 wires would need a longer deck. But if one set is damaged, so would this landing area, so we need 2 runways:

Doubling the size of the flight deck would result in a massive ship, and scaling doesn't favor something getting too big.

Consider the 1967 USS Forrestal fire, even if the deck were to be double the size allowing two landing runways, an attack or an explosion would spread easily across a flat surface and render the whole ship out of action when it comes to air ops.

Note that USS Forrestal was already engaged in combat. But since you have tagged it redundancy, the answer would likely be (although not this site's scope) military planning redundancy, not an engineering one, i.e., if engaged in combat, having more than one carrier is the redundancy to continue engaging in said combat (and land the other planes).

Of course not all freak accidents can be anticipated. Let's say something bad happens to the deck during peacetime, what's the worst that can happen? The airborne aviators unable to land will eject, and the rescue helicopters will bring them back, it's a monetary loss, but not loss of airborne lives.