On paper sure, sounds great. But you take a sub or cruiser, park it off the shores of dirkadirkastan... when the flag goes up they shoot their wad and guess what? They are done. Sail home, spend several weeks in the yards reloading. They are also not a fluid platform. Supporting guys on the ground with a weapon that takes hours to plan (on the fast side) doesn't work.

Take a carrier and it's airwing, park it off the coast, and you can project power ashore for as long as you can keep reloading the boat with bombs, beans and gas (read, indefinately). Support guys on the ground, contain their air assets, run recce, or just punish them mercilessly. A boat and it's airwing is one of the most powerful force projection tools on the planet. The flip side to that, is it's also one of the best humanitarian assets too.