Navies often avoid renaming ships already in service

Why not rename a current Royal Navy ship Ark Royal?

Renaming an existing ship is traditionally considered unlucky, so the Royal Navy normally preserves a commissioned vessel's name.

Traditional Royal Navy practice treats changing a ship's name as bad luck. The Soviet Navy renamed ships more freely, so the custom was not universal even in the twentieth century. British practice carried the superstition forward and used it as one explanation for retaining French names on captured vessels. This was an institutional custom rather than a technical prohibition. A famous name such as Ark Royal is therefore more likely to wait for a new hull than replace the identity of a serving ship.