Carriers are expensive: they imply lots of expensive aircraft, specifically developed just for carrier service, as well as the carrier battle group that trolls around with it.

Plus the logistics pipeline to get fuel and food and such to all that hardware floating around in the ocean.

I have no idea what a carrier costs to operate, but for a normal mega-yacht, it's said to cost about 1/5th original purchase price per year. I'm guessing with the wear and tear on a Navy ship with aircraft banging around on it every few minutes it's something much higher.