Greece has long had a model of state nationalism which, like that of France, treated minorities as a threat to national unity, and pursued assimilation. The Greek Orthodox ethnic minorities of Greece, who had identified with ethnic Greeks as fellow members of the Rum millet, enthusiastically embraced assimilation for the most part.
So there was no enthusiasm through the 19th century for any official status of a language other than Greek, and not many Greek citizens who would think it a good idea. Just as there were not many French citizens who thought official status for Breton or Basque or Occitan or German was a good idea.
In the 20th century, as Greece expanded north, the strife in Ottoman Macedonia between ethnic groups (what Greeks term the Macedonian Struggle) involved various nations as sponsors of those groups. The ethnic free-for-all involved not just ethnic Greeks and Slavs (Macedo-Bulgarians), but also Aromanians. There were Aromanians who identified with Greece, and Aromanians who identified with Bulgaria, and in fact there were Aromanians who identified with Romania.
When the dust settled after the Macedonian Struggle, Romania extracted from the Greek government the concession that Romanian-language schools could operate for Aromanians in Greece. Anecdotally, the villages where Romanian was taught were the villages where Aromanian died out the fastest: the concession made the locals’ allegiance to Greece look suspect.
Official languages other than Greek have never been encouraged in Greece; that has not been the model Greek nationalism has embraced. Talking too loudly about languages other than Greek in Greece has not particularly been favoured either. There is a resurgence of interest in Arvanitika and Aromanian now; but it’s safe for there to be a resurgence, now that the languages are moribund. And unlike the Makedonski of Greece, the loyalty of the Arvanites and the Aromanians to Greece has never been questioned. (An exception for the Aromanians would be the Principality of the Pindus; but that was a marginal phenomenon.)