because A) germany is formable, B) Finland is releasable without modding, C) Netherlands formable too/you can start as them at a later date, D) Ireland also formable.
The thing with Greece is, as i mentioned, that it requires some modding to be in from game start/made formable, this should be in your "reason" to play with them, as it might otherwise leave people confused.
Greek cores appear after 1750.