Kvatch and Anvil are part of Cyrodiil, however not all of Cyrodiil has been added to the game. The reason being clear considering what is present is a 3-way PvP zone. Cyrodiil as a whole cannot be neatly divided into thirds, so only a section of the map which can be neatly divided is included.
Cyrodiil's boundaries have been largely stagnant since it's inception.
There are plans to add in all of Tamriel, so we will see Anvil and Kvatch at a later date.