Sinking an aircraft carrier, let alone most of them, is also such a big loss of life and material, it could easily lead to WW3/nuclear boogaloo.

There are also anti-anti-shipping missile cruisers, CIWS, AWACS, etc. around aircraft carriers all the time.

There is also a lot of stealthy underwater stuff that is indeed ongoing. A big question on that front of course, is how would you know how it’s doing, or what it’s capable of, when it’s by its nature stealthy and hidden.