That was part of the reason that Ranger was kept in reserve as long as she was. But ships rot, even steel ones. Machinery gets way out of date, and must be maintained at certain minimal levels just so that they can be brought back into working condition in a reasonable period of time.
Then you have the physical limitations of the design itself. Catapaults that can’t launch the heaviest of modern aircraft. Arresting wire systems that have the similar problems and so forth.
Finally, these ships get scavanged for parts to keep their sisters in a higher state of readiness. So after a decade or so in reserve, they are little more than hulls.