One of the common ways to refer to the R' Isaac Luria is "the Arizal". I understand this to mean, The Ari, zecher L'bracha (may he be mentioned/remembered for blessing).
However, one usually refers to a Tzaddik (Righteous person) as ZaTZaL, zecher Tzaddik L'bracha.
Why don't we mention that the Ari was a tzaddik when calling him the Arizal?