Because both the Mycenaeans and Greeks (who represent Macedonia) are in this game. This means that Spartans are technically already covered. I think it would be pointless to continue to add Greek civilizations to the game when the need for them is low.
Having many Greek civilizations is integral to ambrox's and Numitor's mod - it's called "Greek Epic".
This mod, however, is called "Ancient World", as is not designed to be so specific to one part of the world. As it is already, it's very ethnocentric in the form of Western and Middle Eastern Empires, which is why in future releases I am thinking about moving a bit Eastward and handling civs such as the Shang Dynasty and maybe the Maurya...Minoans, however, would be historically separate and not already covered in the mod. Also it would give another trading civ into the game - as opposed to another conquest civ. I always welcome new naval civs.
